Group III nitride crystal and method for producing the same

ABSTRACT

A method for producing a group III nitride crystal in the present invention includes the steps of cutting a plurality of group III nitride crystal substrates  10   p  and  10   q  having a main plane from a group III nitride bulk crystal  1 , the main planes  10   pm  and  10   qm  having a plane orientation with an off-angle of five degrees or less with respect to a crystal-geometrically equivalent plane orientation selected from the group consisting of {20-21}, {20-2-1}, {22-41}, and {22-4-1}, transversely arranging the substrates  10   p  and  10   q  adjacent to each other such that the main planes  10   pm  and  10   qm  of the substrates  10   p  and  10   q  are parallel to each other and each [0001] direction of the substrates  10   p  and  10   q  coincides with each other, and growing a group III nitride crystal  20  on the main planes  10   pm  and  10   qm  of the substrates  10   p  and  10   q.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International ApplicationPCT/JP2010/059454, having an international filing date of Jun. 3, 2010,which claims the benefit of priority of Japanese patent application No.2009-154020 filed on Jun. 29, 2009 and the benefit of priority ofJapanese patent application No. 2009-204979 filed on Sep. 4, 2009, eachof which is hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a group III nitride crystal and amethod for producing the group III nitride crystal and also relates to agroup III nitride crystal having a main plane with a plane orientationother than {0001} and a method for producing the group III nitridecrystal.

BACKGROUND ART

Group III nitride crystals suitably used in light emitting devices,electronic devices, and semiconductor sensors are generally produced bycrystal growth on a main plane of a sapphire substrate having a (0001)main plane or a GaAs substrate having a (111) A main plane by avapor-phase growth method, such as a hydride vapor phase epitaxy (HVPE)method or a metalorganic chemical vapor deposition (MOCVD) method, or aliquid-phase growth method, such as a flux method. Thus, group IIInitride crystals generally produced have a main plane with a {0001}plane orientation.

A light emitting device in which a light-emitting layer having amulti-quantum well (MQW) structure is formed on a main plane of a groupIII nitride crystal substrate having the main plane with a {0001} planeorientation generates spontaneous polarization in the light-emittinglayer because of the polarity of the group III nitride crystal in a<0001> direction. The spontaneous polarization reduces luminousefficiency. Thus, there is a demand for the production of a group IIInitride crystal having a main plane with a plane orientation other than{0001}.

The following methods have been proposed as a method for producing agroup III nitride crystal having a main plane with a plane orientationother than {0001}. For example, Japanese Unexamined Patent ApplicationPublication No. 2005-162526 (Patent Literature 1) discloses thefollowing method for producing a GaN crystal having a surface with anyplane orientation independent of the substrate plane orientation. Aplurality of rectangular parallelepiped crystalline masses are cut froma GaN crystal grown by a vapor-phase growth method. After a siliconoxide film is formed on the surface of a sapphire substrate preparedseparately, a plurality of depressions reaching the substrate areformed. The plurality of crystalline masses are embedded in thedepressions such that the top surfaces of the crystalline masses areunidirectionally oriented. Gallium nitride crystals having a surfacewith a certain plane orientation are then grown by a vapor-phase growthmethod using the crystalline masses as seeds.

Japanese Unexamined Patent Application Publication No. 2006-315947(Patent Literature 2) discloses the following method for producing anitride semiconductor wafer that can achieve both a low dislocationdensity and a large area. A primary wafer formed of a hexagonal nitridesemiconductor and having two facing main C planes is prepared. Theprimary wafer is then cut along an M plane to produce a plurality ofnitride semiconductor bars. The plurality of nitride semiconductor barsare then arranged such that the C planes of adjacent nitridesemiconductor bars face each other and the M plane of each of thenitride semiconductor bars becomes the top surface. A nitridesemiconductor is then regrown on the top surfaces of the arrangednitride semiconductor bars to form a nitride semiconductor layer havinga continuous M plane as the main plane.

Japanese Unexamined Patent Application Publication No. 2008-143772(Patent Literature 3) discloses the following method for producing ahigh-crystallinity group III nitride crystal that has a main plane otherthan {0001}. A plurality of group III nitride crystal substrates havinga main plane with a certain plane orientation are cut from a group IIInitride bulk crystal. The substrates are then transversely arrangedadjacent to each other such that the main planes of the substrates areparallel to each other and the substrates have the same [0001]direction. A group III nitride crystal is then grown on the main planesof the substrates.

CITATION LIST

Patent Literature

PTL 1: Japanese Unexamined Patent Application Publication No.2005-162526

PTL 2: Japanese Unexamined Patent Application Publication No.2006-315947

PTL 3: Japanese Unexamined Patent Application Publication No.2008-143772

SUMMARY OF INVENTION Technical Problem

However, in the method according to Japanese Unexamined PatentApplication Publication No. 2005-162526 (Patent Literature 1), in whichGaN crystals are grown using crystalline masses of GaN crystals embeddedin the sapphire substrate as seeds, a difference in thermal expansioncoefficient between sapphire and GaN results in the generation of acrack or strain in the GaN crystals during cooling after crystal growth.Thus, this method could not produce high-crystallinity GaN crystals.

The method according to Japanese Unexamined Patent ApplicationPublication No. 2006-315947 (Patent Literature 2) only produces anitride semiconductor wafer having an M plane as a main plane.Furthermore, when a nitride semiconductor layer is grown using the Mplane as a main plane at a high growth rate, polycrystals are depositedon the main plane. It is therefore difficult to produce a thick nitridesemiconductor layer having high crystallinity.

In the method according to Japanese Unexamined Patent ApplicationPublication No. 2008-143772 (Patent Literature 3), a group III nitridecrystal is grown on a main plane with a certain plane orientation. Thus,the certain plane orientation includes a plane orientation in which acrystal is stably grown and a plane orientation in which a crystal isunstably grown. In the plane orientation in which a crystal is stablygrown, it is difficult to produce a thick group III nitride crystalbecause of a low growth rate of the group III nitride crystal. In theplane orientation in which a crystal is unstably grown, it is difficultto perform stable epitaxial growth of a group III nitride crystal, andthe group III nitride crystal thus grown tends to have a crack.

It is an object of the present invention to solve the problems describedabove and provide a high-crystallinity group III nitride crystal havinga main plane with a plane orientation other than {0001} and a method forproducing a group III nitride crystal in which the group III nitridecrystal can be grown at a high crystal growth rate.

Solution to Problem

The present invention provides a method for producing a group IIInitride crystal includes the steps of: cutting a plurality of group IIInitride crystal substrates having a main plane from a group III nitridebulk crystal, the main plane having a plane orientation with anoff-angle of five degrees or less with respect to acrystal-geometrically equivalent plane orientation selected from thegroup consisting of {20-21}, {20-2-1}, {22-41}, and {22-4-1};transversely arranging the substrates adjacent to each other such thatthe main planes of the substrates are parallel to each other and thesubstrates have the same [0001] direction; and growing a group IIInitride crystal on the main planes of the substrates.

In a method for producing a group III nitride crystal according to thepresent invention, the main planes of the substrates may have a planeorientation with an off-angle of five degrees or less with respect to acrystal-geometrically equivalent plane orientation selected from thegroup consisting of {20-2-1} and {20-21}. The average roughness Ra ofeach contact surface of the substrates adjacent to each other may be 50nm or less. A method for growing the group III nitride crystal may be ahydride vapor phase epitaxy method.

In the step of growing a group III nitride crystal of a method forproducing a group III nitride crystal according to the presentinvention, the crystal growth face of the group III nitride crystal maybe kept flat. In the step of growing a group III nitride crystal on themain planes of the group III nitride crystal substrates, when the planeorientation of the main planes has an off-angle of five degrees or lesswith respect to {20-21}, the group III nitride crystal may have a growthrate below 80 μm/h, when the plane orientation of the main planes has anoff-angle of five degrees or less with respect to {20-2-1}, the groupIII nitride crystal may have a growth rate below 90 μm/h, when the planeorientation of the main planes has an off-angle of five degrees or lesswith respect to {22-41}, the group III nitride crystal may have a growthrate below 60 μm/h, and when the plane orientation of the main planeshas an off-angle of five degrees or less with respect to {22-4-1}, thegroup III nitride crystal may have a growth rate below 80 μm/h.

In the step of growing a group III nitride crystal of a method forproducing a group III nitride crystal according to the presentinvention, the group III nitride crystal may have at least one of thefollowing impurity atom concentrations: an oxygen atom concentration of1×10¹⁶ cm⁻³ or more and 4×10¹⁹ cm⁻³ or less, a silicon atomconcentration of 6×10¹⁴ cm⁻³ or more and 5×10¹⁸ cm⁻³ or less, a hydrogenatom concentration of 6×10¹⁶ cm⁻³ or more and 1×10¹⁸ cm⁻³ or less, and acarbon atom concentration of 1×10¹⁶ cm⁻³ or more and 1×10¹⁸ cm⁻³ orless.

A group III nitride crystal according to the present invention is agroup III nitride crystal having a main plane with acrystal-geometrically equivalent plane orientation selected from thegroup consisting of {20-21}, {20-2-1}, {22-41}, and {22-4-1}. The groupIII nitride crystal has at least one of the following impurity atomconcentrations: an oxygen atom concentration of 1×10¹⁶ cm⁻³ or more and4×10¹⁹ cm⁻³ or less, a silicon atom concentration of 6×10¹⁴ cm⁻³ or moreand 5×10¹⁸ cm⁻³ or less, a hydrogen atom concentration of 6×10¹⁶ cm⁻³ ormore and 1×10¹⁸ cm⁻³ or less, and a carbon atom concentration of 1×10¹⁶cm⁻³ or more and 1×10¹⁸ cm⁻³ or less. The group III nitride crystal mayhave a main plane having an area of 10 cm² or more.

Advantageous Effects of Invention

The present invention can provide a high-crystallinity group III nitridecrystal having a main plane with a plane orientation other than {0001},and a method for producing the group III nitride crystal in which thegroup III nitride crystal can be grown at a high crystal growth rate.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional view illustrating a method forproducing a group III nitride crystal according to an embodiment of thepresent invention. FIG. 1A illustrates the step of cutting group IIInitride crystal substrates, FIG. 1B illustrates the step of arrangingthe group III nitride crystal substrates, FIG. 1C illustrates the stepof growing a group III nitride crystal, and FIG. 1D illustrates the stepof growing an additional group III nitride crystal.

FIG. 2 is a schematic cross-sectional view illustrating a method forproducing a group III nitride crystal according to another embodiment ofthe present invention. FIG. 2A illustrates the step of cutting group IIInitride crystal substrates, FIG. 2B illustrates the step of arrangingthe group III nitride crystal substrates, FIG. 2C illustrates the stepof growing a group III nitride crystal, and FIG. 2D illustrates the stepof growing an additional group III nitride crystal.

FIG. 3 is a schematic cross-sectional view illustrating a method forproducing a group III nitride crystal according to still anotherembodiment of the present invention. FIG. 3A illustrates the step ofcutting group III nitride crystal substrates, FIG. 3B illustrates thestep of arranging the group III nitride crystal substrates, FIG. 3Cillustrates the step of growing a group III nitride crystal, and FIG. 3Dillustrates the step of growing an additional group III nitride crystal.

FIG. 4 is a schematic cross-sectional view illustrating a method forproducing a group III nitride crystal according to still anotherembodiment of the present invention. FIG. 4A illustrates the step ofcutting group III nitride crystal substrates, FIG. 4B illustrates thestep of arranging the group III nitride crystal substrates, FIG. 4Cillustrates the step of growing a group III nitride crystal, and FIG. 4Dillustrates the step of growing an additional group III nitride crystal.

FIG. 5 is a schematic view of a base substrate on which a group IIInitride bulk crystal is to be grown. FIG. 5A is a schematic plan view,and FIG. 5B is a schematic cross-sectional view taken along the lineVB-VB of FIG. 5A.

DESCRIPTION OF EMBODIMENTS

In crystal geometry, indices (Miller indices), such as (hkl) and (hkil),are used to indicate the plane orientation of a crystal face. The planeorientation of a crystal face of a hexagonal crystal, such as a groupIII nitride crystal, is indicated by (hkil), wherein h, k, i, and l areintegers called Miller indices and have the relationship of i=−(h+k). Aplane with the plane orientation (hkil) is referred to as a (hkil)plane. A direction perpendicular to the (hkil) plane (a direction normalto the (hkil) plane) is referred to as a [hkil] direction. {hkil}denotes a generic plane orientation including (hkil) and planeorientations crystal-geometrically equivalent to (hkil). <hkil> denotesa generic direction including [hkik] and directionscrystal-geometrically equivalent to [hkik]

A group III nitride crystal contains group III atomic planes andnitrogen atomic planes alternately disposed in the <0001> direction andconsequently have polarity in the <0001> direction. In the presentapplication, the crystallographic axis is determined such that the groupIII atomic plane is the (0001) plane and the nitrogen atomic plane isthe (000-1) plane.

(First Embodiment)

With reference to FIGS. 1 to 4, a method for producing a group IIInitride crystal according to an embodiment of the present inventionincludes the following steps: cutting a plurality of group III nitridecrystal substrates 10 p and 10 q having main planes 10 pm and 10 qm froma group III nitride bulk crystal 1, the main plane having a planeorientation with an off-angle of five degrees or less with respect to acrystal-geometrically equivalent plane orientation selected from thegroup consisting of {20-21}, {20-2-1}, {22-41}, and {22-4-1}(hereinafter also referred to as a substrate cutting step; see FIGS. 1Ato 4A); transversely arranging the group III nitride crystal substrates10 p and 10 q adjacent to each other such that the main planes 10 pm and10 qm of the group III nitride crystal substrates 10 p and 10 q areparallel to each other and each [0001] direction of the group IIInitride crystal substrates 10 p and 10 q is the same (hereinafter alsoreferred to as a substrate arranging step; see FIGS. 1B to 4B); andgrowing a group III nitride crystal 20 on the main planes 10 pm and 10qm of the substrates 10 p and 10 q (hereinafter also referred to as acrystal growing step; see FIGS. 1C to 4C).

In accordance with a method for producing a group III nitride crystalaccording to the present embodiment, a high-crystallinity group IIInitride crystal having a main plane with a plane orientation other than{0001} can be grown at a high crystal growth rate by growing the groupIII nitride crystal on a plurality of group III nitride crystalsubstrates 10 p and 10 q having the main planes 10 pm and 10 qm with aplane orientation with an off-angle of five degrees or less with respectto a crystal-geometrically equivalent plane orientation selected fromthe group consisting of {20-21}, {20-2-1}, {22-41}, and {22-4-1}.

A method for producing a group III nitride crystal according to thepresent embodiment will be further described in detail below withreference to FIGS. 1 to 4.

With reference to FIGS. 1A to 4A, in the substrate cutting stepaccording to the present embodiment, a plurality of group III nitridecrystal substrates 10 p and 10 q having main planes 10 pm and 10 qm arecut from group III nitride bulk crystal 1. The main planes 10 pm and 10qm have a plane orientation with an off-angle of five degrees or lesswith respect to a crystal-geometrically equivalent plane orientationselected from the group consisting of {20-21}, {20-2-1}, {22-41}, and{22-4-1}. The term “off-angle”, as used herein, refers to an anglebetween one plane orientation and the other plane orientation and can bemeasured by an X-ray diffraction method.

The group III nitride bulk crystal 1 used in the substrate cutting stepis not particularly limited and may be produced by growing a crystal ona main plane of a sapphire substrate having a (0001) main plane or aGaAs substrate having a (111) A plane as a main plane by a commonmethod, for example, a vapor-phase growth method, such as a HVPE methodor a MOCVD method, or a liquid-phase growth method, such as a fluxmethod. Thus, the group III nitride bulk crystal generally, but notalways, has a {0001} main plane. In order to reduce dislocation densityand increase crystallinity, the group III nitride bulk crystal 1 ispreferably grown by a facet growth method, as disclosed in JapaneseUnexamined Patent Application Publication No. 2001-102307. In the facetgrowth method, a facet is formed on a plane on which a crystal is to begrown (a crystal growth face) and the crystal is grown without embeddingthe facet.

A plurality of group III nitride crystal substrates 10 p and 10 q havingthe main planes 10 pm and 10 qm with a plane orientation with anoff-angle of five degrees or less with respect to acrystal-geometrically equivalent plane orientation selected from thegroup consisting of {20-21}, {20-2-1}, {22-41}, and {22-4-1} may be cutfrom the group III nitride bulk crystal 1 by any method. For example, asillustrated in FIGS. 1A to 4A, the group III nitride crystal substrates10 p and 10 q may be cut from the group III nitride bulk crystal 1 atpredetermined intervals along a plurality of planes perpendicular to oneof the <20-21> direction, the <20-2-1> direction, the <22-41> direction,and the <22-4-1> direction (These planes have a plane orientationcrystal-geometrically equivalent to one of {20-21}, {20-2-1}, {22-41},and {22-4-1}. The same applies hereinafter.)

As illustrated in FIGS. 1B to 4B, in the substrate arranging stepaccording to the present embodiment, the plurality of group III nitridecrystal substrates 10 p and 10 q cut out are transversely arrangedadjacent to each other such that the main planes 10 pm and 10 qm of thesubstrates 10 p and 10 q are parallel to each other and each [0001]direction of the substrates 10 p and 10 q is the same. In FIGS. 1B to4B, although reference signs are given to two adjacent group III nitridecrystal substrates 10 p and 10 q of the plurality of group III nitridecrystal substrates, the same applies to other adjacent group III nitridecrystal substrates.

Variations in the angle between the crystallographic axis and the mainplanes of the plurality of group III nitride crystal substrates 10 p and10 q within the main planes result in a inhomogeneous composition of thegroup III nitride crystal grown on the main planes of the substrates 10p and 10 q within planes parallel to the main planes of the substrates10 p and 10 q. The substrates 10 p and 10 q are therefore transverselyarranged such that the main planes 10 pm and 10 qm of the substrates 10p and 10 q are parallel to each other. The main planes 10 pm and 10 qmof the substrates 10 p and 10 q parallel to each other do notnecessarily lie in the same plane. The height difference ΔT (not shown)between the main planes 10 pm and 10 qm of the adjacent two group IIInitride crystal substrates 10 p and 10 q is preferably 0.1 mm or less,more preferably 0.01 mm or less.

In order to unidirectionally arrange the crystal orientation of theplurality of group III nitride crystal substrates 10 p and 10 q toachieve more uniform crystal growth, the substrates 10 p and 10 q aretransversely arranged such that each [0001] direction of the substrates10 p and 10 q is the same. A gap between the plurality of group IIInitride crystal substrates 10 p and 10 q results in low crystallinity ofcrystals grown on the gap. The group III nitride crystal substrates 10 pand 10 q are therefore arranged in contact with each other.

With reference to FIGS. 1A to 4A and FIGS. 1B to 4B, the substratecutting step and the substrate arranging step yield the plurality ofgroup III nitride crystal substrates 10 p and 10 q from the group IIInitride bulk crystal 1. The group III nitride crystal substrates 10 pand 10 q are transversely arranged such that the main planes 10 pm and10 qm of the plurality of group III nitride crystal substrates 10 p and10 q are parallel to each other and each [0001] direction of thesubstrates 10 p and 10 q is the same. The group III nitride crystalsubstrates 10 p and 10 q have the main planes 10 pm and 10 qm with aplane orientation with an off-angle of five degrees or less with respectto a crystal-geometrically equivalent plane orientation selected fromthe group consisting of {20-21}, {20-2-1}, {22-41}, and {22-4-1}.

With reference to FIGS. 1C to 4C, in the crystal growing step accordingto the present embodiment, a group III nitride crystal 20 is grown onthe main planes 10 pm and 10 qm of the plurality of group III nitridecrystal substrates 10 p and 10 q. The group III nitride crystal 20 isgrown by epitaxial growth.

The main planes 10 pm and 10 qm of the plurality of group III nitridecrystal substrates 10 p and 10 q have a plane orientation with anoff-angle of five degrees or less with respect to acrystal-geometrically equivalent plane orientation selected from thegroup consisting of {20-21}, {20-2-1}, {22-41}, and {22-4-1}. Thus, amain plane 20 m of the group III nitride crystal 20 epitaxially grown onthe main planes 10 pm and 10 qm has the same plane orientation as themain planes 10 pm and 10 qm of the plurality of group III nitridecrystal substrates 10 p and 10 q (that is, a plane orientation with anoff-angle of five degrees or less with respect to acrystal-geometrically equivalent plane orientation selected from thegroup consisting of {20-21}, {20-2-1}, {22-41}, and {22-4-1}).

Since the group III nitride crystal 20 is grown on the main planes 10 pmand 10 qm of the plurality of group III nitride crystal substrates 10 pand 10 q, and the substrates 10 p and 10 q and the group III nitridecrystal 20 grown have a small difference in thermal expansioncoefficient, a crack and strain rarely occur in the group III nitridecrystal 20 during cooling after crystal growth, thus yielding ahigh-crystallinity group III nitride crystal.

From the perspective described above, the plurality of group III nitridecrystal substrates 10 p and 10 q and the group III nitride crystal 20grown preferably have the same chemical composition. These steps canyield a high-crystallinity group III nitride crystal 20 having the mainplane 20 m with a plane orientation with an off-angle of five degrees orless with respect to a crystal-geometrically equivalent planeorientation selected from the group consisting of {20-21}, {20-2-1},{22-41}, and {22-4-1}.

In the method for producing a group III nitride crystal according to thepresent embodiment, the main planes 10 pm and 10 qm of the plurality ofgroup III nitride crystal substrates 10 p and 10 q have a planeorientation with an off-angle of five degrees or less with respect to acrystal-geometrically equivalent plane orientation selected from thegroup consisting of {20-21}, {20-2-1}, {22-41}, and {22-4-1}. Thus, thehigh-crystallinity group III nitride crystal 20 having the main plane 20m with a plane orientation with an off-angle of five degrees or lesswith respect to a crystal-geometrically equivalent plane orientationselected from the group consisting of {20-21}, {20-2-1}, {22-41}, and{22-4-1} can be stably grown on the main planes 10 pm and 10 qm of theplurality of group III nitride crystal substrates 10 p and 10 q at ahigh crystal growth rate.

The group III nitride crystal 20 thus formed has a large crystalthickness and consequently a high degree of freedom of cuttingdirection. Thus, a group III nitride crystal and a group III nitridecrystal substrate having any plane orientation other than thecrystal-geometrically equivalent plane orientation selected from thegroup consisting of {20-21}, {20-2-1}, {22-41}, and {22-4-1} can beformed.

When the plane orientation of the main planes 10 pm and 10 qm of theplurality of group III nitride crystal substrates 10 p and 10 q has anoff-angle above five degrees with respect to a crystal-geometricallyequivalent plane orientation selected from the group consisting of{20-21}, {20-2-1}, {22-41}, and {22-4-1}, it is difficult to stably growa high-crystallinity group III nitride crystal on the main planes 10 pmand 10 qm.

In the method for producing a group III nitride crystal according to thepresent embodiment, in order to more stably grow a group III nitridecrystal 20 having higher crystallinity at a higher crystal growth rate,the main planes 10 pm and 10 qm of the plurality of group III nitridecrystal substrates 10 p and 10 q preferably have a plane orientationwith an off-angle of five degrees or less with respect to acrystal-geometrically equivalent plane orientation selected from thegroup consisting of {20-2-1} and {20-21}.

In the method for producing a group III nitride crystal according to thepresent embodiment, each of the contact surfaces (hereinafter referredto as contact surfaces 10 pt and 10 qt) of the plurality of group IIInitride crystal substrates 10 p and 10 q adjacent to each otherpreferably has an average roughness Ra of 50 nm or less, more preferably5 nm or less. When each of the contact surfaces 10 pt and 10 qt has anaverage roughness Ra above 50 nm, a region of the group III nitridecrystal 20 on the neighborhood of the contact surfaces 10 pt and 10 qt(hereinafter referred to as a region-on-substrate-interface 20 t) haslow crystallinity.

The region-on-substrate-interface 20 t is disposed on both sides of avertical plane 20 tc extending upward from one end of the substratecontact surfaces 10 pt and 10 qt. The width ΔW of theregion-on-substrate-interface 20 t depends on the average surfaceroughness Ra of the contact surfaces 10 pt and 10 qt and the growthconditions and crystallinity of the group III nitride crystal. The widthΔW ranges from approximately 10 to 1000 μm. A region-on-substrate 20 s(A region on the plurality of group III nitride crystal substrates 10 pand 10 q other than the region-on-substrate-interface. The same applieshereinafter.) and the region-on-substrate-interface 20 t can bedifferentiated by comparing the full widths at half maximum of X-raydiffraction peaks and/or the threading dislocation densities of the mainplanes in these regions.

The average surface roughness Ra refers to the arithmetical meanroughness Ra defined in JIS B 0601. More specifically, in a portionhaving a reference length taken from a roughness profile in thedirection of an average line, the total of distances between the averageline and the roughness profile (absolute deviations) is averaged overthe reference length. The average surface roughness Ra can be measuredwith an atomic force microscope (AFM).

In order for the contact surfaces 10 pt and 10 qt of the plurality ofgroup III nitride crystal substrates 10 p and 10 q to have an averageroughness Ra of 50 nm or less, the method for producing a group IIInitride crystal according to the present embodiment preferably includesthe step of grinding and/or polishing side surfaces of the plurality ofgroup III nitride crystal substrates 10 p and 10 q serving as thecontact surfaces 10 pt and 10 qt (hereinafter referred to as agrinding/polishing step) after the substrate cutting step and before thesubstrate arranging step.

In order to further increase the crystallinity of a group III nitridecrystal to be grown, the method for producing a group III nitridecrystal according to the present embodiment preferably further includesthe step of grinding and/or polishing the main planes 10 pm and 10 qm,on which a group III nitride crystal is to be grown, of the plurality ofgroup III nitride crystal substrates 10 p and 10 q (a grinding/polishingstep) after the substrate cutting step and before the substratearranging step. After the grinding/polishing step, each of the mainplanes 10 pm and 10 qm preferably has a surface roughness of 50 nm orless, more preferably 5 nm or less.

In the method for producing a group III nitride crystal according to thepresent embodiment, a method for growing the group III nitride crystal20 is not particularly limited and may be a common method, for example,a vapor-phase growth method, such as a HVPE method or a MOCVD method, ora liquid-phase growth method, such as a flux method. Among theseproduction methods, the HVPE method is preferred because of a highcrystal growth rate.

With reference to FIGS. 1C to 4C, the left side of a central wavy lineindicates the case where the group III nitride crystal 20 grows andforms a flat main plane 20 m while a crystal growth face 20 g is keptflat, and the right side of the central wavy line indicates the casewhere the group III nitride crystal 20 grows while forming a pluralityof facets 20 gf on the crystal growth face 20 g and forms a main plane20 m having a plurality of facets 20 mf.

With reference to the left side of the central wavy line in FIGS. 1C to4C, in the step of growing a group III nitride crystal in the method forproducing a group III nitride crystal according to the presentembodiment, the group III nitride crystal 20 is preferably grown whilethe crystal growth face 20 g is kept flat. The clause “the crystalgrowth face 20 g is kept flat”, as used herein, means that the crystalgrowth face 20 g is substantially flat and forms no facet 20 gf.

In the step of growing a group III nitride crystal according to thepresent embodiment, the group III nitride crystal 20 is grown on themain planes 10 pm and 10 qm of the plurality of group III nitridecrystal substrates 10 p and 10 q. The main planes 10 pm and 10 qm have aplane orientation with an off-angle of five degrees or less with respectto a crystal-geometrically equivalent plane orientation selected fromthe group consisting of {20-21}, {20-2-1}, {22-41}, and {22-4-1}. Thegroup III nitride crystal grows in one of the <20-21> direction, the<20-2-1> direction, the <22-41> direction, and the <22-4-1> direction.The group III nitride crystal 20 grown in that direction tends to have aplanar defect in the {0001} plane (since the (0001) in-plane and the(000-1) in-plane are the same in-plane, they are hereinaftercollectively referred to as the {0001} in-plane) and low crystallinity.

With reference to the right side of the central wavy line in FIGS. 1C to4C, a particular increase in the growth rate of the group III nitridecrystal 20 results in the formation of a plurality of facets 20 gf onthe crystal growth face 20 g, which is accompanied by an increase in thedensity of planar defects in the {0001} plane, resulting in lowcrystallinity.

Thus, in the growth of the group III nitride crystal 20, keeping thecrystal growth face 20 g flat without forming a plurality of facets 20gf on the crystal growth face 20 g can reduce the density of planardefects in the {0001} plane of the group III nitride crystal 20 grown,thereby yielding a high-crystallinity group III nitride crystal. Thedensity of planar defects in the {0001} plane of the group III nitridecrystal may be determined by cathodoluminescence (CL) of a cross sectionperpendicular to the direction of the main plane of the group IIInitride crystal tilting from the (0001) plane or the (000-1) plane.

In the growth of the group III nitride crystal 20, the crystal growthface 20 g can be kept flat at a growth rate of the group III nitridecrystal 20 below a predetermined rate. The growth rate at which thecrystal growth face 20 g can be kept flat depends on the planeorientation of the main planes 10 pm and 10 qm of the plurality of groupIII nitride crystal substrates 10 p and 10 q as described below. Whenthe plane orientation of the main planes of the group III nitridecrystal substrates has an off-angle of five degrees or less with respectto {20-21}, the growth rate of the group III nitride crystal is below 80μm/h. When the plane orientation of the main planes of the group IIInitride crystal substrates has an off-angle of five degrees or less withrespect to {20-2-1}, the growth rate of the group III nitride crystal isbelow 90 μm/h. When the plane orientation of the main planes of thegroup III nitride crystal substrates has an off-angle of five degrees orless with respect to {22-41}, the growth rate of the group III nitridecrystal is below 60 μm/h. When the plane orientation of the main planesof the group III nitride crystal substrates has an off-angle of fivedegrees or less with respect to {22-4-1}, the growth rate of the groupIII nitride crystal is below 80 μm/h.

In the growth of a group III nitride crystal, when the growth rate ofthe group III nitride crystal 20 is equal to or more than thepredetermined rate, a plurality of facets 20 gf are formed on thecrystal growth face 20 g of the group III nitride crystal 20. Theplurality of facets 20 gf have the shape of a plurality of stripes. Eachof the stripe-shaped facets 20 gf extends in a direction perpendicularto the direction of the crystal growth face 20 g tilting from the (0001)plane or the (000-1) plane. Each stripe of the facets 20 gf has a widthand a depth in the range of approximately 2 to 300 μm. The formation ofthe facets 20 gf on the crystal growth face 20 g during the growth ofthe group III nitride crystal 20 causes planar defects in the {0001}plane of the group III nitride crystal 20, thus decreasingcrystallinity. A plurality of facets 20 mf formed on the main plane 20 mof the group III nitride crystal 20 during such growth have a shape, adirection, a width, and a depth similar to those of the plurality offacets 20 gf formed on the crystal growth face 20 g. The group IIInitride crystal 20 has depressions 20 v formed of the plurality offacets 20 mf in the main plane 20 m.

In the step of growing a group III nitride crystal, a group III nitridecrystal 20 having at least one of the following impurity atomconcentrations is preferably grown: an oxygen atom concentration of1×10¹⁶ cm⁻³ or more and 4×10¹⁹ cm⁻³ or less, a silicon atomconcentration of 6×10¹⁴ cm⁻³ or more and 5×10¹⁸ cm⁻³ or less, a hydrogenatom concentration of 6×10¹⁶ cm⁻³ or more and 1×10¹⁸ cm⁻³ or less, and acarbon atom concentration of 1×10¹⁶ cm⁻³ or more and 1×10¹⁸ cm⁻³ orless. The concentrations of the impurity atoms of a group III nitridecrystal, such as an oxygen atom, a silicon atom, a hydrogen atom, and acarbon atom can be measured by secondary ion mass spectrometry(hereinafter also referred to as SIMS).

Setting at least one impurity concentration of the oxygen atomconcentration, the silicon atom concentration, the hydrogen atomconcentration, and the carbon atom concentration of a group III nitridecrystal to the predetermined concentration described above can reducethe density of planar defects in the {0001} plane, yielding ahigh-crystallinity group III nitride crystal. Coalescence ofdislocations in the growth of a group III nitride crystal reduces thenumber of dislocations and the volume of the crystal, thereby warpingthe crystal and increasing planar defects. Setting the impurity atomconcentration to the predetermined concentration described aboveprobably reduces the decrease in crystal volume, reducing the density ofplanar defects. At an impurity atom concentration below thepredetermined concentration, the decrease in crystal volume cannotprobably be reduced, which makes it difficult to reduce the formation ofplanar defects in the {0001} plane. On the other hand, at an impurityatom concentration above the predetermined concentration, impurity atomsare probably condensed in the (0001) plane, making it difficult toreduce the formation of planar defects in the {0001} plane.

From the perspective described above, the oxygen atom concentration ismore preferably 5×10¹⁶ cm⁻³ or more and 1×10¹⁹ cm⁻³ or less, still morepreferably 1×10¹⁷ cm⁻³ or more and 8×10¹⁸ cm⁻³ or less. The silicon atomconcentration is more preferably 1×10¹⁵ cm⁻³ or more and 3×10¹⁸ cm⁻³ orless, still more preferably 1×10¹⁶ cm⁻³ or more and 1×10¹⁸ cm⁻³ or less.The hydrogen atom concentration is more preferably 1×10¹⁷ cm⁻³ or moreand 9×10¹⁷ cm⁻³ or less, still more preferably 2×10¹⁷ cm⁻³ or more and7×10¹⁷ cm⁻³ or less. The carbon atom concentration is more preferably5×10¹⁶ cm⁻³ or more and 9×10¹⁷ cm⁻³ or less, still more preferably9×10¹⁶ cm⁻³ or more and 7×10¹⁷ cm⁻³ or less.

In order to further reduce the formation of planar defects in the {0001}plane during the growth of a group III nitride crystal, more preferablytwo, still more preferably three, most preferably four, of the impurityatom concentrations described above (the oxygen atom concentration, thesilicon atom concentration, the hydrogen atom concentration, and thecarbon atom concentration) satisfy the predetermined concentrations.

In a method for growing a group III nitride crystal, an impurity atommay be added to a group III nitride crystal by any method, including thefollowing methods. Oxygen atoms may be added using O₂ gas (oxygen gas),O₂ gas diluted with an inert gas, such as N₂ gas, Ar gas, or He gas, acarrier gas (such as H₂ gas or N₂ gas) containing H₂O, or a raw materialgas (such as HCl gas or NH₃ gas) containing H₂O. A quartz container maybe used as a crystal growth container to allow quartz of the reactionvessel to react with a raw material NH₃ gas, producing H₂O gas to beused. Silicon atoms may be added using a silicon compound gas, such asSiH₄ gas, SiH₃Cl gas, SiH₂Cl₂ gas, SiHCl₃ gas, SiCl₄ gas, or SiF₄. Aquartz container may be used as a crystal growth container to allowquartz of the reaction vessel to react with a raw material NH₃ gas,producing a silicon-containing gas to be used. Hydrogen atoms may beadded using a gas mixture of a carrier gas, such as H₂ gas, and an inertgas, such as N₂ gas, Ar gas, or He gas. Carbon atoms may be added usinga carbon compound gas, such as CH₄ gas. A carbon material (for example,a carbon plate) may be placed in a crystal growth container to allowcarbon of the carbon material to react with hydrogen gas serving as acarrier gas or HN₃ gas serving as a raw material gas, producing acarbon-containing gas to be used.

A method for preventing the contamination of a group III nitride crystalwith an impurity atom may be the following method. The contaminationwith oxygen atoms and silicon atoms may be prevented by not using a gascontaining oxygen atoms and silicon atoms and covering the inner wall ofa crystal growth container containing oxygen atoms and/or silicon atomswith a material containing neither oxygen atoms nor silicon atoms, suchas BN. The contamination with hydrogen atoms may be prevented by notusing a carrier gas containing hydrogen gas. The contamination withcarbon atoms may be prevented by using neither a carbon material nor agas containing carbon atoms.

With reference to FIGS. 1C to 4C and FIGS. 1D to 4D, a method forproducing a group III nitride crystal according to the presentembodiment may include the steps of preparing an additional group IIInitride crystal substrate 20 p having a main plane 20 pm from the groupIII nitride crystal 20 grown as described above, the main plane 20 pmhaving a plane orientation with an off-angle of five degrees or lesswith respect to a crystal-geometrically equivalent plane orientationselected from the group consisting of {20-21}, {20-2-1}, {22-41}, and{22-4-1}, and growing an additional group III nitride crystal 30 on themain plane 20 pm of the additional group III nitride crystal substrate20 p. These steps can yield an additional high-crystallinity group IIInitride crystal 30 having the main plane 30 m with a plane orientationwith an off-angle of five degrees or less with respect to acrystal-geometrically equivalent plane orientation selected from thegroup consisting of {20-21}, {20-2-1}, {22-41}, and {22-4-1}.

The step for preparing an additional group III nitride crystal substrate20 p is not particularly limited and may be performed by cutting a planeparallel to the main planes 10 pm and 10 qm of the plurality of groupIII nitride crystal substrates 10 p and 10 q from the group III nitridecrystal 20 grown. In order to grow an additional group III nitridecrystal 30 having high crystallinity on the main plane 20 pm, the mainplane 20 pm of the additional group III nitride crystal substrate 20 pthus cut out preferably has an average roughness Ra of 50 nm or less,more preferably 5 nm or less. In order for the main plane 20 pm of thegroup III nitride crystal substrate 20 p to have an average roughness Raof 50 nm or less, after the group III nitride crystal substrate 20 p iscut out and before the additional group III nitride crystal 30 is grown,the main plane 20 pm of the group III nitride crystal substrate 20 p ispreferably ground and/or polished.

In the method for producing a group III nitride crystal according to thepresent embodiment, a method for growing the additional group IIInitride crystal 30 is not particularly limited and may be a commonmethod, for example, a vapor-phase growth method, such as a HVPE methodor a MOCVD method, or a liquid-phase growth method, such as a fluxmethod. Among these production methods, the HVPE method is preferredbecause of a high crystal growth rate.

With reference to FIGS. 1D to 4D, the left side of a central wavy lineindicates the case where the group III nitride crystal 30 grows andforms a flat main plane 30 m while a crystal growth face 30 g is keptflat, and the right side of the central wavy line indicates the casewhere the group III nitride crystal 30 grows while forming a pluralityof facets 30 gf on the crystal growth face 30 g and forms a main plane30 m having a plurality of facets 30 mf.

With reference to the left side of the central wavy line in FIGS. 1D to4D, in the step of growing an additional group III nitride crystal inthe method for producing a group III nitride crystal according to thepresent embodiment, the additional group III nitride crystal 30 ispreferably grown while the crystal growth face 30 g is kept flat. Theclause “the crystal growth face 30 g is kept flat”, as used herein,means that the crystal growth face 30 g is substantially flat and formsno facet 30 gf.

Also in the growth of the additional group III nitride crystal 30according to the present embodiment, the additional group III nitridecrystal 30 grown in one of the <20-21> direction, the <20-2-1>direction, the <22-41> direction, and the <22-4-1> direction tends tohave a planar defect in the {0001} plane and low crystallinity.

With reference to the right side of the central wavy line in FIGS. 1D to4D, a particular increase in the growth rate of the additional group IIInitride crystal 30 results in the formation of a plurality of facets 30gf on the crystal growth face 30 g, which is accompanied by an increasein the density of planar defects in the {0001} plane, resulting in lowcrystallinity.

Thus, in the growth of the additional group III nitride crystal 30,keeping the crystal growth face 30 g flat without forming a plurality offacets 30 gf on the crystal growth face 30 g can reduce the density ofplanar defects in the {0001} plane of the additional group III nitridecrystal 30 grown, thereby yielding a high-crystallinity group IIInitride crystal.

In the growth of the additional group III nitride crystal 30, thecrystal growth face 30 g can be kept flat at a growth rate of theadditional group III nitride crystal 30 below a predetermined rate. Thegrowth rate at which the crystal growth face 30 g can be kept flatdepends on the plane orientation of the main plane 20 pm of theadditional group III nitride crystal substrate 20 p as described below.When the plane orientation of the main plane of the additional group IIInitride crystal substrate has an off-angle of five degrees or less withrespect to {20-21}, the growth rate of the additional group III nitridecrystal is below 140 μm/h. When the plane orientation of the main planeof the additional group III nitride crystal substrate has an off-angleof five degrees or less with respect to {20-2-1}, the growth rate of theadditional group III nitride crystal is below 150 μm/h. When the planeorientation of the main plane of the additional group III nitridecrystal substrate has an off-angle of five degrees or less with respectto {22-41}, the growth rate of the additional group III nitride crystalis below 120 μm/h. When the plane orientation of the main plane of theadditional group III nitride crystal substrate has an off-angle of fivedegrees or less with respect to {22-4-1}, the growth rate of theadditional group III nitride crystal is below 140 μm/h.

Thus, even at a high crystal growth rate, the crystal growth face ismore easily kept flat in the growth of the additional group III nitridecrystal 30 than in the growth of the group III nitride crystal 20. Thisis probably because the group III nitride crystal 20 is grown on themain planes 10 pm and 10 qm of the adjacent group III nitride crystalsubstrates 10 p and 10 q whereas the additional group III nitridecrystal 30 is grown on the main plane 20 pm of the additional group IIInitride crystal substrate 20 p and can consequently be grown moreuniformly over the entire surface of the substrate.

In the growth of the additional group III nitride crystal, when thegrowth rate of the additional group III nitride crystal 30 is equal toor more than the predetermined rate, a plurality of facets 30 gf areformed on the crystal growth face 30 g of the additional group IIInitride crystal 30. The plurality of facets 30 gf have the shape of aplurality of stripes. Each of the stripe-shaped facets 30 gf extends ina direction perpendicular to the direction of the crystal growth face 30g tilting from the (0001) plane or the (000-1) plane. Each stripe of thefacets 30 gf has a width and a depth in the range of approximately 2 to300 μm. The formation of the facets 20 gf on the crystal growth face 20g during the growth of the group III nitride crystal 20 causes planardefects in the {0001} plane of the group III nitride crystal 20, thusdecreasing crystallinity. A plurality of facets 30 mf formed on the mainplane 30 m of the group III nitride crystal 30 during growth have ashape, a direction, a width, and a depth similar to those of theplurality of facets 30 gf formed on the crystal growth face 30 g. Thegroup III nitride crystal 30 has depressions 30 v formed of theplurality of facets 30 mf in the main plane 30 m.

In the step of growing the additional group III nitride crystal 30, asin the growth of the group III nitride crystal 20, the group III nitridecrystal 30 having at least one of the following impurity atomconcentrations is preferably grown: an oxygen atom concentration of1×10¹⁶ cm⁻³ or more and 4×10¹⁹ cm⁻³ or less, a silicon atomconcentration of 6×10¹⁴ cm⁻³ or more and 5×10¹⁸ cm⁻³ or less, a hydrogenatom concentration of 6×10¹⁶ cm⁻³ or more and 1×10¹⁸ cm⁻³ or less, and acarbon atom concentration of 1×10¹⁶ cm⁻³ or more and 1×10¹⁸ cm⁻³ orless.

From the perspective described above, with respect to the impurity atomconcentration of the group III nitride crystal 30, the oxygen atomconcentration is more preferably 5×10¹⁶ cm⁻³ or more and 1×10¹⁹ cm⁻³ orless, still more preferably 1×10¹⁷ cm⁻³ or more and 8×10¹⁸ cm⁻³ or less.The silicon atom concentration is more preferably 1×10¹⁵ cm⁻³ or moreand 3×10¹⁸ cm⁻³ or less, still more preferably 1×10¹⁶ cm⁻³ or more and1×10¹⁸ cm⁻³ or less. The hydrogen atom concentration is more preferably1×10¹⁷ cm⁻³ or more and 9×10¹⁷ cm⁻³ or less, still more preferably2×10¹⁷ cm⁻³ or more and 7×10¹⁷ cm⁻³ or less. The carbon atomconcentration is more preferably 5×10¹⁶ cm⁻³ or more and 9×10¹⁷ cm⁻³ orless, still more preferably 9×10¹⁶ cm⁻³ or more and 7×10¹⁷ cm⁻³ or less.More preferably two, still more preferably three, most preferably four,of the impurity atom concentrations described above (the oxygen atomconcentration, the silicon atom concentration, the hydrogen atomconcentration, and the carbon atom concentration) satisfy thepredetermined concentrations.

In a method for growing an additional group III nitride crystal, amethod for adding an impurity atom to the additional group III nitridecrystal 30 and a method for preventing the contamination of theadditional group III nitride crystal 30 with an impurity atom are notparticularly limited. The methods described for the growth of the groupIII nitride crystal 20 can be used.

In the growth of an additional group III nitride crystal, aregion-on-substrate 30 s of the additional group III nitride crystal 30can be formed on the region-on-substrate 20 s of the additional groupIII nitride crystal substrate 20 p, and a region-on-substrate-interface30 t of the additional group III nitride crystal 30 can be formed on theregion-on-substrate-interface 20 t of the additional group III nitridecrystal substrate 20 p.

(Second Embodiment)

With reference to FIGS. 1 to 4, a group III nitride crystal according toanother embodiment of the present invention is group III nitridecrystals 20 and 30 having a main plane with a crystal-geometricallyequivalent plane orientation selected from the group consisting of{20-21}, {20-2-1}, {22-41}, and {22-4-1}. The group III nitride crystals20 and 30 have at least one of the following impurity atomconcentrations: an oxygen atom concentration of 1×10¹⁶ cm⁻³ or more and4×10¹⁹ cm⁻³ or less, a silicon atom concentration of 6×10¹⁴ cm⁻³ or moreand 5×10¹⁸ cm⁻³ or less, a hydrogen atom concentration of 6×10¹⁶ cm⁻³ ormore and 1×10¹⁸ cm⁻³ or less, and a carbon atom concentration of 1×10¹⁶cm⁻³ or more and 1×10¹⁸ cm⁻³ or less.

The group III nitride crystals 20 and 30 according to the presentembodiment have main planes 20 m and 30 m with a crystal-geometricallyequivalent plane orientation selected from the group consisting of{20-21}, {20-2-1}, {22-41}, and {22-4-1}. In a light emitting device inwhich a light-emitting layer having a multi-quantum well (MQW) structureis formed on the main planes 20 m and 30 m of the group III nitridecrystals 20 and 30 serving as a substrate, therefore, spontaneouspolarization in the light-emitting layer is prevented. This reduces adecrease in luminous efficiency. The group III nitride crystalsaccording to the present embodiment have at least one of the followingimpurity concentrations: an oxygen atom concentration of 1×10¹⁶ cm⁻³ ormore and 4×10¹⁹ cm⁻³ or less, a silicon atom concentration of 6×10¹⁴cm⁻³ or more and 5×10¹⁸ cm⁻³ or less, a hydrogen atom concentration of6×10¹⁶ cm⁻³ or more and 1×10¹⁸ cm⁻³ or less, and a carbon atomconcentration of 1×10¹⁶ cm⁻³ or more and 1×10¹⁸ cm⁻³ or less. Thus, thegroup III nitride crystals according to the present embodiment have highcrystallinity due to a reduced formation of planar defects in the {0001}plane.

The group III nitride crystals 20 and 30 according to the presentembodiment have the main planes 20 m and 30 m preferably having an areaof 10 cm² or more, more preferably 18 cm² or more, still more preferably40 cm² or more. The group III nitride crystals thus obtained have alarge size and high crystallinity.

EXAMPLES

[Preparation of Group III Nitride Bulk Crystal]

A GaN bulk crystal, which is a group III nitride bulk crystal for use ina method for producing a group III nitride crystal according to thepresent invention, was produced by the following method, with referenceto FIG. 5.

First, a SiO₂ layer having a thickness of 100 nm was formed as a masklayer 91 on a base substrate 90 by sputtering. The base substrate 90 wasa GaAs substrate having a (111) A plane as a main plane and had adiameter of 50 mm and a thickness of 0.8 mm. As illustrated in FIGS. 5Aand B, a pattern was then formed by a photolithography method andetching. In the pattern, windows 91 w having a diameter D of 2 μm werehexagonally close-packed at intervals P of 4 μm. The GaAs substrate (thebase substrate 90) was exposed from the windows 91 w.

A GaN bulk crystal, which is a group III nitride bulk crystal, was grownon the GaAs substrate (the base substrate 90), on which the mask layer91 having a plurality of windows 91 w was formed, by a HVPE method. Morespecifically, a GaN low-temperature layer having a thickness of 80 nmwas grown at 500° C. on the GaAs substrate by the HVPE method. A GaNintermediate layer having a thickness of 60 μm was then grown at 950° C.A GaN bulk crystal having a thickness of 5 mm was then grown at 1050° C.

The GaAs substrate was then removed from the GaN bulk crystal by etchingusing aqua regia to form a GaN bulk crystal having a diameter of 50 mmand a thickness of 3 mm, which is a group III nitride bulk crystal.

Example 1

First, with reference to FIG. 1A, both main planes, a (0001) plane and a(000-1) plane, of a GaN bulk crystal (a group III nitride bulk crystal1) were ground and polished to an average roughness Ra of 5 nm. Theaverage surface roughness Ra was determined with AFM.

With reference to FIG. 1A, the GaN bulk crystal (the group III nitridebulk crystal 1) in which the average roughness Ra of each of the mainplanes was 5 nm was cut perpendicularly to the <20-21> direction into aplurality of GaN crystal substrates (group III nitride crystalsubstrates 10 p and 10 q). The GaN crystal substrates had a width S of3.1 mm, a length L in the range of 20 to 50 mm, and a thickness T of 1mm and had a {20-21} main plane. The four planes of each of the GaNcrystal substrates not yet subjected to grinding and polishing wereground and polished to an average roughness Ra of 5 nm. Thus, aplurality of GaN crystal substrates were prepared in which the averageroughness Ra of the {20-21} main plane was 5 nm. In some of the GaNcrystal substrates, the plane orientation of the main plane did notprecisely coincide with {20-21}. In all such GaN crystal substrates,however, the plane orientation of the main plane had an off-angle offive degrees or less with respect to {20-21}. The off-angle wasdetermined by an X-ray diffraction method.

With reference to FIG. 1B, the plurality of GaN crystal substrates weretransversely arranged adjacent to each other in a quartz crystal growthcontainer such that (20-21) main planes 10 pm and 10 qm of the GaNcrystal substrates (the group III nitride crystal substrates 10 p and 10q) were parallel to each other and each [0001] direction of the GaNcrystal substrates (the group III nitride crystal substrates 10 p and 10q) coincided with each other. Also with reference to FIG. 1C, each ofcontact surfaces 10 pt and 10 qt of the plurality of GaN crystalsubstrates (the group III nitride crystal substrates 10 p and 10 q) hadan average roughness Ra of 5 nm. A circle inscribed in the plurality ofGaN crystal substrates (the group III nitride crystal substrates 10 pand 10 q) thus arranged had a diameter of 50 mm.

With reference to FIG. 1C, the (20-21) main planes 10 pm and 10 qm ofthe plurality of GaN crystal substrates (the group III nitride crystalsubstrates 10 p and 10 q) arranged in the quartz crystal growthcontainer were treated at 800° C. for two hours in a mixed gasatmosphere of 10% by volume hydrogen chloride gas and 90% by volumenitrogen gas. A GaN crystal (a group III nitride crystal 20) was thengrown on the main planes 10 pm and 10 qm by a HVPE method at a crystalgrowth temperature of 1020° C. for 40 hours.

The GaN crystal (the group III nitride crystal 20) had a thickness of2.4 mm, as determined by a contact thickness gauge (Digimatic Indicatormanufactured by Mitutoyo Co.). Thus, the crystal growth rate was 60μm/h. With reference to the left side of the central portion in FIG. 1C,the GaN crystal (the group III nitride crystal 20) had no abnormalcrystal growth in a region-on-substrate-interface 20 t and aregion-on-substrate 20 s and had a flat (20-21) main plane 20 m. Thecrystallinity of the GaN crystal (the group III nitride crystal 20) wasdetermined by the X-ray rocking curve measurement of the (20-21) plane.In the region-on-substrate 20 s of the GaN crystal, an unsplitdiffraction peak having a full width at half maximum of 100 arcsec wasobserved. In the region-on-substrate-interface 20 t having a width ΔW of300 μm, a split diffraction peak having a full width at half maximum of300 arcsec was observed.

The (20-21) main plane 20 m of the GaN crystal had a threadingdislocation density of 1×10⁷ cm⁻² in the region-on-substrate 20 s and3×10⁷ cm⁻² in the region-on-substrate-interface 20 t, as determined bycathodoluminescence (hereinafter referred to as CL). The planar defectdensity in the {0001} plane of the GaN crystal was determined to be 8.3cm⁻¹ by cathodoluminescence (CL) of a cross section of the GaN crystalperpendicular to the <1-210> direction. The GaN crystal had a carrierconcentration of 5×10¹⁸ cm⁻³ as calculated from the Hall measurement.The concentrations of the main impurity atoms of the GaN crystal weremeasured by secondary ion mass spectrometry (SIMS)) as follows: theoxygen atom concentration [O] was 5×10¹⁸ cm⁻³, the silicon atomconcentration [Si] was 1×10¹⁸ cm⁻³, the hydrogen atom concentration [H]was 4×10¹⁶ cm⁻³, and the carbon atom concentration [C] was 5×10¹⁵ cm⁻³.Table I summarizes the results.

Although all the plane orientations of the main planes of the pluralityof GaN crystal substrates on which a GaN crystal was grown were (20-21)in Example 1, substantially the same results were obtained even in thecase that at least part of the plane orientations were (−2201) (which iscrystal-geometrically equivalent with (20-21)).

Example 2

First, with reference to FIG. 2A, both main planes, a (0001) plane and a(000-1) plane, of a GaN bulk crystal (a group III nitride bulk crystal1) were ground and polished to an average roughness Ra of 5 nm.

With reference to FIG. 2A, the GaN bulk crystal (the group III nitridebulk crystal 1) in which the average roughness Ra of each of the mainplanes was 5 nm was cut perpendicularly to the <20-2-1> direction into aplurality of GaN crystal substrates (group III nitride crystalsubstrates 10 p and 10 q). The GaN crystal substrates had a width S of3.1 mm, a length L in the range of 20 to 50 mm, and a thickness T of 1mm and had a {20-2-1} main plane. Four planes of each of the GaN crystalsubstrates not subjected to grinding and polishing were ground andpolished to an average roughness Ra of 5 nm. Thus, a plurality of GaNcrystal substrates were prepared in which the average roughness Ra ofthe {20-2-1} main plane was 5 nm. In some of the GaN crystal substrates,the plane orientation of the main plane did not precisely coincide with{20-2-1}. In all such GaN crystal substrates, however, the planeorientation of the main plane had an off-angle of five degrees or lesswith respect to {20-2-1}.

With reference to FIG. 2B, the plurality of GaN crystal substrates weretransversely arranged adjacent to each other in a quartz crystal growthcontainer such that (20-2-1) main planes 10 pm and 10 qm of the GaNcrystal substrates (the group III nitride crystal substrates 10 p and 10q) were parallel to each other and each [0001] direction of the GaNcrystal substrates (the group III nitride crystal substrates 10 p and 10q) coincided with each other. Also with reference to FIG. 2C, each ofcontact surfaces 10 pt and 10 qt of the plurality of GaN crystalsubstrates (the group III nitride crystal substrates 10 p and 10 q) hadan average roughness Ra of 5 nm. A circle inscribed in the plurality ofGaN crystal substrates (the group III nitride crystal substrates 10 pand 10 q) thus arranged had a diameter of 50 mm.

With reference to FIG. 2C, the (20-2-1) main planes 10 pm and 10 qm ofthe plurality of GaN crystal substrates (the group III nitride crystalsubstrates 10 p and 10 q) arranged in the quartz crystal growthcontainer were treated in the same way as in Example 1. A GaN crystal (agroup III nitride crystal 20) was then grown on the main planes 10 pmand 10 qm by the same growth method at the same growth temperature forthe same growth time as in Example 1.

The GaN crystal (the group III nitride crystal 20) had a thickness of3.2 mm, and the crystal growth rate was 80 μm/h. With reference to theleft side of the central portion in FIG. 2C, the GaN crystal (the groupIII nitride crystal 20) had no abnormal crystal growth in aregion-on-substrate-interface 20 t and a region-on-substrate 20 s andhad a flat (20-2-1) main plane 20 m. The crystallinity of the GaNcrystal (the group III nitride crystal 20) was determined by the X-rayrocking curve measurement of the (20-2-1) plane. In theregion-on-substrate 20 s, an unsplit diffraction peak having a fullwidth at half maximum of 90 arcsec was observed. Thus, this GaN crystalhad better crystallinity than the GaN crystal having the (20-21) planeas the main plane. In the region-on-substrate-interface 20 t having awidth ΔW of 100 μm, a split diffraction peak having a full width at halfmaximum of 360 arcsec was observed.

The (20-2-1) main plane 20 m of the GaN crystal had a threadingdislocation density of 1×10⁷ cm⁻² in the region-on-substrate 20 s and4×10⁷ cm⁻² in the region-on-substrate-interface 20 t. The planar defectdensity in the {0001} plane of the GaN crystal was determined to be 6.1cm⁻¹ by cathodoluminescence (CL) of a cross section of the GaN crystalperpendicular to the <1-210> direction. The GaN crystal had a carrierconcentration of 1×10¹⁸ cm⁻³ as calculated from the Hall measurement.The concentrations of the main impurity atoms of the GaN crystal weremeasured by secondary ion mass spectrometry (SIMS)) as follows: theoxygen atom concentration [O] was 9×10¹⁷ cm⁻³, the silicon atomconcentration [Si] was 1×10¹⁸ cm⁻³, the hydrogen atom concentration [H]was 4×10¹⁶ cm⁻³, and the carbon atom concentration [C] was 5×10¹⁵ cm⁻³.Table I summarizes the results.

Although all the plane orientations of the main planes of the pluralityof GaN crystal substrates on which a GaN crystal was grown were (20-2-1)in Example 2, substantially the same results were obtained even in thecase that at least part of the plane orientations were (−202-1) (whichis crystal-geometrically equivalent with (20-2-1)).

The GaN crystal produced in Example 2 had a lower formation of cracksthan the GaN crystal produced in Example 1.

Example 3

First, with reference to FIG. 3A, both main planes, a (0001) plane and a(000-1) plane, of the GaN bulk crystal (a group III nitride bulk crystal1) were ground and polished to an average roughness Ra of 5 nm.

With reference to FIG. 3A, the GaN bulk crystal (the group III nitridebulk crystal 1) in which the average roughness Ra of each of the mainplanes was 5 nm was cut perpendicularly to the <22-41> direction into aplurality of GaN crystal substrates (group III nitride crystalsubstrates 10 p and 10 q). The GaN crystal substrates had a width S of3.2 mm, a length L in the range of 20 to 50 mm, and a thickness T of 1mm and had a {22-41} main plane. Four planes of each of the GaN crystalsubstrates not subjected to grinding and polishing were ground andpolished to an average roughness Ra of 5 nm. Thus, a plurality of GaNcrystal substrates were prepared in which the average roughness Ra ofthe {22-41} main plane was 5 nm. In some of the GaN crystal substrates,the plane orientation of the main plane did not precisely coincide with{22-41}. In all such GaN crystal substrates, however, the planeorientation of the main plane had an off-angle of five degrees or lesswith respect to {22-41}.

With reference to FIG. 3B, the plurality of GaN crystal substrates weretransversely arranged adjacent to each other in a quartz crystal growthcontainer such that (22-41) main planes 10 pm and 10 qm of the GaNcrystal substrates (the group III nitride crystal substrates 10 p and 10q) were parallel to each other and each [0001] direction of the GaNcrystal substrates (the group III nitride crystal substrates 10 p and 10q) coincided with each other. Also with reference to FIG. 3C, each ofcontact surfaces 10 pt and 10 qt of the plurality of GaN crystalsubstrates (the group III nitride crystal substrates 10 p and 10 q) hadan average roughness Ra of 5 nm. A circle inscribed in the plurality ofGaN crystal substrates (the group III nitride crystal substrates 10 pand 10 q) thus arranged had a diameter of 50 mm.

With reference to FIG. 3C, the (22-41) main planes 10 pm and 10 qm ofthe plurality of GaN crystal substrates (the group III nitride crystalsubstrates 10 p and 10 q) arranged in the quartz crystal growthcontainer were treated in the same way as in Example 1. A GaN crystal (agroup III nitride crystal 20) was then grown on the main planes 10 pmand 10 qm by the same growth method at the same growth temperature forthe same growth time as in Example 1.

The GaN crystal (the group III nitride crystal 20) had a thickness of3.0 mm, and the crystal growth rate was 75 μm/h. With reference to theright side of the central portion in FIG. 3C, the GaN crystal (the groupIII nitride crystal 20) had a (22-41) main plane 20 m in aregion-on-substrate-interface 20 t and a region-on-substrate 20 s. Aplurality of facets 20 mf on the (22-41) main plane 20 m formeddepressions 20 v. The crystallinity of the GaN crystal (the group IIInitride crystal 20) was determined by the X-ray rocking curvemeasurement of the (22-41) plane. In the region-on-substrate 20 s, anunsplit diffraction peak having a full width at half maximum of 120arcsec was observed. In the region-on-substrate-interface 20 t having awidth ΔW of 300 μm, a split diffraction peak having a full width at halfmaximum of 220 arcsec was observed.

The (22-41) main plane 20 m of the GaN crystal had a threadingdislocation density of 3×10⁷ cm⁻² in the region-on-substrate 20 s and7×10⁷ cm⁻² in the region-on-substrate-interface 20 t. The planar defectdensity in the {0001} plane of the GaN crystal was determined to be 8.6cm⁻¹ by cathodoluminescence (CL) of a cross section of the GaN crystalperpendicular to the <10-10> direction. The GaN crystal had a carrierconcentration of 2×10¹⁸ cm⁻³ as calculated from the Hall measurement.The concentrations of the main impurity atoms of the GaN crystal weremeasured by secondary ion mass spectrometry (SIMS)) as follows: theoxygen atom concentration [O] was 2×10¹⁸ cm⁻³, the silicon atomconcentration [Si] was 9×10¹⁷ cm⁻³, the hydrogen atom concentration [H]was 4×10¹⁶ cm⁻³, and the carbon atom concentration [C] was 5×10¹⁵ cm⁻³.Table I summarizes the results.

Although all the plane orientations of the main planes of the pluralityof GaN crystal substrates on which a GaN crystal was grown were (22-41)in Example 3, substantially the same results were obtained even in thecase that at least part of the plane orientations were (−4221) (which iscrystal-geometrically equivalent with (22-41)).

Example 4

First, with reference to FIG. 4A, both main planes, a (0001) plane and a(000-1) plane, of the GaN bulk crystal (a group III nitride bulk crystal1) were ground and polished to an average roughness Ra of 5 nm.

With reference to FIG. 4A, the GaN bulk crystal (the group III nitridebulk crystal 1) in which the average roughness Ra of each of the mainplanes was 5 nm was cut perpendicularly to the <22-4-1> direction into aplurality of GaN crystal substrates (group III nitride crystalsubstrates 10 p and 10 q). The GaN crystal substrates had a width S of3.2 mm, a length L in the range of 20 to 50 mm, and a thickness T of 1mm and had a {22-4-1} main plane. Four planes of each of the GaN crystalsubstrates not subjected to grinding and polishing were ground andpolished to an average roughness Ra of 5 nm. Thus, a plurality of GaNcrystal substrates were prepared in which the average roughness Ra ofthe {22-4-1} main plane was 5 nm. In some of the GaN crystal substrates,the plane orientation of the main plane did not precisely coincide with{22-4-1}. In all such GaN crystal substrates, however, the planeorientation of the main plane had an off-angle of five degrees or lesswith respect to {22-4-1}.

With reference to FIG. 4B, the plurality of GaN crystal substrates weretransversely arranged adjacent to each other in a quartz crystal growthcontainer such that (22-4-1) main planes 10 pm and 10 qm of the GaNcrystal substrates (the group III nitride crystal substrates 10 p and 10q) were parallel to each other and each [0001] direction of the GaNcrystal substrates (the group III nitride crystal substrates 10 p and 10q) coincided with each other. Also with reference to FIG. 4C, each ofcontact surfaces 10 pt and 10 qt of the plurality of GaN crystalsubstrates (the group III nitride crystal substrates 10 p and 10 q) hadan average roughness Ra of 5 nm. A circle inscribed in the plurality ofGaN crystal substrates (the group III nitride crystal substrates 10 pand 10 q) thus arranged had a diameter of 50 mm.

With reference to FIG. 4C, the (22-4-1) main planes 10 pm and 10 qm ofthe plurality of GaN crystal substrates (the group III nitride crystalsubstrates 10 p and 10 q) arranged in the quartz crystal growthcontainer were treated in the same way as in Example 1. A GaN crystal (agroup III nitride crystal 20) was then grown on the main planes 10 pmand 10 qm by the same growth method at the same growth temperature forthe same growth time as in Example 1.

The GaN crystal (the group III nitride crystal 20) had a thickness of4.0 mm, and the crystal growth rate was 100 μm/h. With reference to theright side of the central portion in FIG. 4C, the GaN crystal (the groupIII nitride crystal 20) had a (22-4-1) main plane 20 m in aregion-on-substrate-interface 20 t and a region-on-substrate 20 s. Aplurality of facets 20 mf on the (22-4-1) main plane 20 m formeddepressions 20 v. The crystallinity of the GaN crystal (the group IIInitride crystal 20) was determined by the X-ray rocking curvemeasurement of the (22-4-1) plane. In the region-on-substrate 20 s, anunsplit diffraction peak having a full width at half maximum of 140arcsec was observed. In the region-on-substrate-interface 20 t having awidth ΔW of 500 μm, a split diffraction peak having a full width at halfmaximum of 200 arcsec was observed.

The (22-4-1) main plane 20 m of the GaN crystal had a threadingdislocation density of 3×10⁷ cm⁻² in the region-on-substrate 20 s and7×10⁷ cm⁻² in the region-on-substrate-interface 20 t. The planar defectdensity in the {0001} plane of the GaN crystal was determined to be 7.9cm⁻¹ by cathodoluminescence (CL) of a cross section of the GaN crystalperpendicular to the <10-10> direction. The GaN crystal had a carrierconcentration of 2×10¹⁸ cm⁻³ as calculated from the Hall measurement.The concentrations of the main impurity atoms of the GaN crystal weremeasured by secondary ion mass spectrometry (SIMS)) as follows: theoxygen atom concentration [O] was 2×10¹⁸ cm⁻³, the silicon atomconcentration [Si] was 9×10¹⁷ cm⁻³, the hydrogen atom concentration [H]was 4×10¹⁶ cm⁻³, and the carbon atom concentration [C] was 5×10¹⁵ cm⁻³.Table I summarizes the results.

Although all the plane orientations of the main planes of the pluralityof GaN crystal substrates on which a GaN crystal was grown were (22-4-1)in Example 4, substantially the same results were obtained even in thecase that at least part of the plane orientations were (−422-1) (whichis crystal-geometrically equivalent with (22-4-1)).

TABLE I Example 1 Example 2 Example 3 Example 4 Group III Type ofsubstrate GaN GaN GaN GaN nitride Plane orientation of main plane(20-21) (20-2-1) (22-41) (22-4-1) crystal Surface roughness Ra of mainplane (mm) 5 5 5 5 substrate Surface roughness Ra of adjacent plane (mm)5 5 5 5 Group III Type of crystal GaN GaN GaN GaN nitride Crystal growthmethod HVPE HVPE HVPE HVPE crystal Crystal growth temperature (° C.)1020 1020 1020 1020 Crystal growth rate (μm/hr) 60 80 75 100 Planeorientation of main plane (20-21) (20-2-1) (22-41) (22-4-1) Presence ofdepression in main plane No No Yes Yes Full width at halfRegion-on-substrate 100 90 120 140 maximum of X-ray Region-on-substrate-300 360 220 200 diffraction peak (arcsec) interface Threadingdislocation Region-on-substrate 1 × 10⁷  1 × 10⁷  3 × 10⁷  3 × 10⁷ density of main plane Region-on-substrate- 3 × 10⁷  4 × 10⁷  7 × 10⁷  7× 10⁷  (cm⁻²) interface Planar defect density (cm⁻¹) 8.3 6.1 8.6 7.9Carrier concentration (cm⁻³) 5 × 10¹⁸ 1 × 10¹⁸ 2 × 10¹⁸ 2 × 10¹⁸ Mainimpurity atoms [O] (cm⁻³) 5 × 10¹⁸ 9 × 10¹⁷ 2 × 10¹⁸ 2 × 10¹⁸ [Si](cm⁻³) 1 × 10¹⁸ 1 × 10¹⁸ 9 × 10¹⁷ 9 × 10¹⁷ [H] (cm⁻³) 4 × 10¹⁶ 4 × 10¹⁶4 × 10¹⁶ 4 × 10¹⁶ [C] (cm⁻³) 5 × 10¹⁵ 5 × 10¹⁵ 5 × 10¹⁵ 5 × 10¹⁵

As is clear from Table I, a high-crystallinity group III nitride crystalhaving a main plane with a plane orientation other than {0001} can begrown at a high crystal growth rate by growing the group III nitridecrystal on a plurality of group III nitride crystal substrates 10 phaving the main planes 10 pm and 10 qm with a plane orientation with anoff-angle of five degrees or less with respect to acrystal-geometrically equivalent plane orientation selected from thegroup consisting of {20-21}, {20-2-1}, {22-41}, and {22-4-1}.

Comparative Example 1

A plurality of GaN crystal substrates (group III nitride crystalsubstrates) in which a {1-100} main plane had an average roughness Ra of5 nm were produced in the same way as in Example 1 except that the GaNbulk crystal (group III nitride bulk crystal) was cut along a pluralityof planes perpendicular to the <1-100> direction. In some of the GaNcrystal substrates, the plane orientation of the main plane did notprecisely coincide with {1-100}. In all such GaN crystal substrates,however, the plane orientation of the main plane had an off-angle offive degrees or less with respect to {1-100}. The off-angle wasdetermined by an X-ray diffraction method.

The plurality of GaN crystal substrates were transversely arrangedadjacent to each other in a quartz crystal growth container such that(1-100) main planes of the GaN crystal substrates (group III nitridecrystal substrates) were parallel to each other and each [0001]direction of the GaN crystal substrates (group III nitride crystalsubstrates) coincided with each other. Each of the contact surfaces ofthe plurality of GaN crystal substrates (group III nitride crystalsubstrates) had an average roughness Ra of 5 nm. A circle inscribed inthe plurality of GaN crystal substrates (the group III nitride crystalsubstrates 10 p and 10 q) thus arranged had a diameter of 50 mm.

The (1-100) main planes of the plurality of GaN crystal substrates(group III nitride crystal substrates) arranged in the quartz crystalgrowth container were treated in the same way as in Example 1. A GaNcrystal (group III nitride crystal) was then grown on the main planes bythe same growth method at the same growth temperature for the samegrowth time as in Example 1.

The GaN crystal (group III nitride crystal) had a thickness of 0.8 mm,and the crystal growth rate was 20 μm/h. The GaN crystal (group IIInitride crystal) had no abnormal crystal growth also in theregion-on-substrate-interface 20 t and had a (1-100) main plane. Thecrystallinity of the GaN crystal (group III nitride crystal) wasdetermined by the X-ray rocking curve measurement of the (1-100) plane.In the region-on-substrate of the GaN crystal, an unsplit diffractionpeak having a full width at half maximum of 100 arcsec was observed. Inthe region-on-substrate-interface having a width ΔW of 300 μm, a splitdiffraction peak having a full width at half maximum of 300 arcsec wasobserved.

The (1-100) main plane of the GaN crystal had a threading dislocationdensity of 1×10⁷ cm⁻² in the region-on-substrate and 3×10⁷ cm⁻² in theregion-on-substrate-interface. The GaN crystal had a carrierconcentration of 5×10¹⁸ cm⁻³. The main impurity atoms of the GaN crystalwere oxygen (O) atoms and silicon (Si) atoms. Table II summarizes theresults.

Although all the plane orientations of the main planes of the pluralityof GaN crystal substrates on which a GaN crystal was grown were (1-100)in Comparative Example 1, substantially the same results were obtainedeven in the case that at least part of the plane orientations were(−1100) (which is crystal-geometrically equivalent with (1-100)).

Comparative Example 2

A plurality of GaN crystal substrates (group III nitride crystalsubstrates) in which a {11-20} main plane had an average roughness Ra of5 nm were produced in the same way as in Example 1 except that the GaNbulk crystal (group III nitride bulk crystal) was cut along a pluralityof planes perpendicular to the <11-20> direction. In some of the GaNcrystal substrates, the plane orientation of the main plane did notprecisely coincide with {11-20}. In all such GaN crystal substrates,however, the plane orientation of the main plane had an off-angle offive degrees or less with respect to {11-20}. The off-angle wasdetermined by an X-ray diffraction method.

The plurality of GaN crystal substrates were transversely arrangedadjacent to each other in a quartz crystal growth container such that(11-20) main planes of the GaN crystal substrates (group III nitridecrystal substrates) were parallel to each other and each [0001]direction of the GaN crystal substrates (group III nitride crystalsubstrates) coincided with each other. Each of the contact surfaces ofthe plurality of GaN crystal substrates (group III nitride crystalsubstrates) had an average roughness Ra of 5 nm. A circle inscribed inthe plurality of GaN crystal substrates (the group III nitride crystalsubstrates 10 p and 10 q) thus arranged had a diameter of 50 mm.

The (11-20) main planes of the plurality of GaN crystal substrates(group III nitride crystal substrates) arranged in the quartz crystalgrowth container were treated in the same way as in Example 1. A GaNcrystal (group III nitride crystal) was then grown on the main planes bythe same growth method at the same growth temperature for the samegrowth time as in Example 1.

The GaN crystal (group III nitride crystal) had a thickness of 0.8 mm,and the crystal growth rate was 20 μm/h. The GaN crystal (group IIInitride crystal) had no abnormal crystal growth also in theregion-on-substrate-interface 20 t and had a (11-20) main plane. Thecrystallinity of the GaN crystal (the group III nitride crystal) wasdetermined by the X-ray rocking curve measurement of the (11-20) plane.In the region-on-substrate of the GaN crystal, an unsplit diffractionpeak having a full width at half maximum of 250 arcsec was observed. Inthe region-on-substrate-interface having a width ΔW of 300 μm, a splitdiffraction peak having a full width at half maximum of 620 arcsec wasobserved.

The (11-20) main plane of the GaN crystal had a threading dislocationdensity of 1×10⁷ cm⁻² in the region-on-substrate and 8×10⁷ cm⁻² in theregion-on-substrate-interface. The GaN crystal had a carrierconcentration of 5×10¹⁸ cm⁻³. The main impurity atoms of the GaN crystalwere oxygen (O) atoms and silicon (Si) atoms. Table II summarizes theresults.

Although all the plane orientations of the main planes of the pluralityof GaN crystal substrates on which a GaN crystal was grown were (11-20)in Comparative Example 2, substantially the same results were obtainedeven in the case that at least part of the plane orientations were(−1-120) (which is crystal-geometrically equivalent with (11-20)).

Comparative Example 3

A plurality of GaN crystal substrates (group III nitride crystalsubstrates) in which a {1-102} main plane had an average roughness Ra of5 nm were produced in the same way as in Example 1 except that the GaNbulk crystal (group III nitride bulk crystal) was cut along a pluralityof planes perpendicular to the <1-102> direction. In some of the GaNcrystal substrates, the plane orientation of the main plane did notprecisely coincide with {1-102}. In all such GaN crystal substrates,however, the plane orientation of the main plane had an off-angle offive degrees or less with respect to {1-102}. The off-angle wasdetermined by an X-ray diffraction method.

The plurality of GaN crystal substrates were transversely arrangedadjacent to each other in a quartz crystal growth container such that(1-102) main planes of the GaN crystal substrates (group III nitridecrystal substrates) were parallel to each other and each [0001]direction of the GaN crystal substrates (group III nitride crystalsubstrates) coincided with each other. Each of the contact surfaces ofthe plurality of GaN crystal substrates (group III nitride crystalsubstrates) had an average roughness Ra of 5 nm. A circle inscribed inthe plurality of GaN crystal substrates (the group III nitride crystalsubstrates 10 p and 10 q) thus arranged had a diameter of 50 mm.

The (1-102) main planes of the plurality of GaN crystal substrates(group III nitride crystal substrates) arranged in the quartz crystalgrowth container were treated in the same way as in Example 1. A GaNcrystal (group III nitride crystal) was then grown on the main planes bythe same growth method at the same growth temperature for the samegrowth time as in Example 1.

The GaN crystal (group III nitride crystal) had a thickness of 0.8 mm,and the crystal growth rate was 20 μm/h. The GaN crystal (group IIInitride crystal) had no abnormal crystal growth also in theregion-on-substrate-interface 20 t and had a (1-102) main plane. Thecrystallinity of the GaN crystal (the group III nitride crystal) wasdetermined by the X-ray rocking curve measurement of the (1-102) plane.In the region-on-substrate of the GaN crystal, an unsplit diffractionpeak having a full width at half maximum of 120 arcsec was observed. Inthe region-on-substrate-interface having a width ΔW of 300 μm, a splitdiffraction peak having a full width at half maximum of 480 arcsec wasobserved.

The (1-102) main plane of the GaN crystal had a threading dislocationdensity of 1×10⁷ cm⁻² in the region-on-substrate and 6×10⁷ cm⁻² in theregion-on-substrate-interface. The GaN crystal had a carrierconcentration of 5×10¹⁸ cm⁻³. The main impurity atoms of the GaN crystalwere oxygen (O) atoms and silicon (Si) atoms. Table II summarizes theresults.

Although all the plane orientations of the main planes of the pluralityof GaN crystal substrates on which a GaN crystal was grown were (1-102)in Comparative Example 3, substantially the same results were obtainedeven in the case that at least part of the plane orientations were(−1102) (which is crystal-geometrically equivalent with (1-102)).

Comparative Example 4

A plurality of GaN crystal substrates (group III nitride crystalsubstrates) in which a {11-22} main plane had an average roughness Ra of5 nm were produced in the same way as in Example 1 except that the GaNbulk crystal (group III nitride bulk crystal) was cut along a pluralityof planes perpendicular to the <11-22> direction. In some of the GaNcrystal substrates, the plane orientation of the main plane did notprecisely coincide with {11-22}. In all such GaN crystal substrates,however, the plane orientation of the main plane had an off-angle offive degrees or less with respect to {11-22}. The off-angle wasdetermined by an X-ray diffraction method.

The plurality of GaN crystal substrates were transversely arrangedadjacent to each other in a quartz crystal growth container such that(11-22) main planes of the GaN crystal substrates (group III nitridecrystal substrates) were parallel to each other and each [0001]direction of the GaN crystal substrates (group III nitride crystalsubstrates) coincided with each other. Each of the contact surfaces ofthe plurality of GaN crystal substrates (group III nitride crystalsubstrates) had an average roughness Ra of 5 nm. A circle inscribed inthe plurality of GaN crystal substrates (the group III nitride crystalsubstrates 10 p and 10 q) thus arranged had a diameter of 50 mm.

The (11-22) main planes of the plurality of GaN crystal substrates(group III nitride crystal substrates) arranged in the quartz crystalgrowth container were treated in the same way as in Example 1. A GaNcrystal (group III nitride crystal) was then grown on the main planes bythe same growth method at the same growth temperature for the samegrowth time as in Example 1.

The GaN crystal (group III nitride crystal) had a thickness of 0.8 mm,and the crystal growth rate was 20 μm/h. The GaN crystal (group IIInitride crystal) had no abnormal crystal growth also in theregion-on-substrate-interface 20 t and had a (11-22) main plane. Thecrystallinity of the GaN crystal (group III nitride crystal) wasdetermined by the X-ray rocking curve measurement of the (11-22) plane.In the region-on-substrate of the GaN crystal, an unsplit diffractionpeak having a full width at half maximum of 90 arcsec was observed. Inthe region-on-substrate-interface having a width ΔW of 500 μm, a splitdiffraction peak having a full width at half maximum of 380 arcsec wasobserved.

The (11-22) main plane of the GaN crystal had a threading dislocationdensity of 1×10⁷ cm⁻² in the region-on-substrate and 4×10⁷ cm⁻² in theregion-on-substrate-interface. The GaN crystal had a carrierconcentration of 5×10¹⁸ cm⁻³. The main impurity atoms of the GaN crystalwere oxygen (O) atoms and silicon (Si) atoms. Table II summarizes theresults.

Although all the plane orientations of the main planes of the pluralityof GaN crystal substrates on which a GaN crystal was grown were (11-22)in Comparative Example 4, substantially the same results were obtainedeven in the case that at least part of the plane orientations were(−1-122) (which is crystal-geometrically equivalent with (11-22)).

Comparative Example 5

A plurality of GaN crystal substrates (group III nitride crystalsubstrates) in which a {12-30} main plane had an average roughness Ra of5 nm were produced in the same way as in Example 1 except that the GaNbulk crystal (group III nitride bulk crystal) was cut along a pluralityof planes perpendicular to the <12-30> direction. In some of the GaNcrystal substrates, the plane orientation of the main plane did notprecisely coincide with {12-30}. In all such GaN crystal substrates,however, the plane orientation of the main plane had an off-angle offive degrees or less with respect to {12-30}. The off-angle wasdetermined by an X-ray diffraction method.

The plurality of GaN crystal substrates were transversely arrangedadjacent to each other in a quartz crystal growth container such that(12-30) main planes of the GaN crystal substrates (group III nitridecrystal substrates) were parallel to each other and each [0001]direction of the GaN crystal substrates (group III nitride crystalsubstrates) coincided with each other. Each of the contact surfaces ofthe plurality of GaN crystal substrates (group III nitride crystalsubstrates) had an average roughness Ra of 5 nm. A circle inscribed inthe plurality of GaN crystal substrates (the group III nitride crystalsubstrates 10 p and 10 q) thus arranged had a diameter of 50 mm.

The (12-30) main planes of the plurality of GaN crystal substrates(group III nitride crystal substrates) arranged in the quartz crystalgrowth container were treated in the same way as in Example 1. A GaNcrystal (group III nitride crystal) was then grown on the main planes bythe same growth method at the same growth temperature for the samegrowth time as in Example 1.

The GaN crystal (group III nitride crystal) had a thickness of 0.8 mm,and the crystal growth rate was 20 μm/h. The GaN crystal (group IIInitride crystal) had no abnormal crystal growth also in theregion-on-substrate-interface 20 t and had a (12-30) main plane. Thecrystallinity of the GaN crystal (group III nitride crystal) wasdetermined by the X-ray rocking curve measurement of the (12-30) plane.In the region-on-substrate of the GaN crystal, an unsplit diffractionpeak having a full width at half maximum of 280 arcsec was observed. Inthe region-on-substrate-interface having a width ΔW of 500 μm, a splitdiffraction peak having a full width at half maximum of 660 arcsec wasobserved.

The (12-30) main plane of the GaN crystal had a threading dislocationdensity of 1×10⁷ cm⁻² in the region-on-substrate and 7×10⁷ cm⁻² in theregion-on-substrate-interface. The GaN crystal had a carrierconcentration of 4×10¹⁸ cm⁻³. The main impurity atoms of the GaN crystalwere oxygen (O) atoms and silicon (Si) atoms. Table II summarizes theresults.

Although all the plane orientations of the main planes of the pluralityof GaN crystal substrates on which a GaN crystal was grown were (12-30)in Comparative Example 5, substantially the same results were obtainedeven in the case that at least part of the plane orientations were(−1-230) (which is crystal-geometrically equivalent with (12-30)).

TABLE II Comparative Comparative Comparative Comparative ComparativeExample 1 Example 2 Example 3 Example 4 Example 5 Group III Type ofsubstrate GaN GaN GaN GaN GaN nitride Plane orientation of main plane(1-100) (11-20) (1-102) (11-22) (12-30) crystal Surface roughness Ra ofmain plane (mm) 5 5 5 5 5 substrate Surface roughness Ra of adjacentplane (mm) 5 5 5 5 5 Group III Type of crystal GaN GaN GaN GaN GaNnitride Crystal growth method HVPE HVPE HVPE HVPE HVPE crystal Crystalgrowth temperature (° C.) 1020 1020 1020 1020 1020 Crystal growth rate(μm/hr) 20 20 20 20 20 Plane orientation of main plane (1-100) (11-20)(1-102) (11-22) (12-30) Presence of depression in main plane No Yes NoNo Yes Full width at half maximum Region-on-substrate 100 250 120 90 280of X-ray diffraction peak Region-on- 300 620 480 380 660 (arcsec)substrate-interface Threading dislocation Region-on-substrate 1 × 10⁷  1× 10⁷  1 × 10⁷  1 × 10⁷  1 × 10⁷  density of main plane (cm⁻²)Region-on- 3 × 10⁷  8 × 10⁷  6 × 10⁷  4 × 10⁷  7 × 10⁷ substrate-interface Carrier concentration (cm⁻³) 5 × 10¹⁸ 5 × 10¹⁸ 5 ×10¹⁸ 5 × 10¹⁸ 4 × 10¹⁸ Main impurity atoms O, Si O, Si O, Si O, Si O, Si

With reference to Tables I and II, the use of a plurality of group IIInitride crystal substrates having a main plane with a plane orientationof {1-100}, {11-20}, {1-102}, {11-22}, or {12-30} also yielded ahigh-crystallinity group III nitride crystal having a main plane with aplane orientation other than {0001} but resulted in a lower crystalgrowth rate than the use of a plurality of group III nitride crystalsubstrates having a main plane with a plane orientation of {20-21},{20-2-1}, {22-41}, or {22-4-1}.

Examples 5 to 8

In Example 5, a GaN crystal (group III nitride crystal) was grown in thesame way as in Example 1 except that the inner wall of the quartzcrystal growth container was covered with a BN plate and the crystalgrowth rate was 70 μm/h. In Example 6, a GaN crystal (group III nitridecrystal) was grown in the same way as in Example 5 except that thecrystal growth rate was 80 μm/h. In Example 7, a GaN crystal (group IIInitride crystal) was grown in the same way as in Example 5 except thatO₂ gas diluted with N₂ gas, SiCl₄ gas, H₂ gas, and CH₄ gas were used toadd high concentrations of oxygen atoms, silicon atoms, hydrogen atoms,and carbon atoms to the GaN crystal. In Example 8, a GaN crystal (groupIII nitride crystal) was grown in the same way as in Example 7 exceptthat the crystal growth rate was 80 μm/h. Table III summarizes theresults.

Examples 9 to 12

In Example 9, a GaN crystal (group III nitride crystal) was grown in thesame way as in Example 2 except that the inner wall of the quartzcrystal growth container was covered with a BN plate. In Example 10, aGaN crystal (group III nitride crystal) was grown in the same way as inExample 9 except that the crystal growth rate was 90 μm/h. In Example11, a GaN crystal (group III nitride crystal) was grown in the same wayas in Example 9 except that O₂ gas diluted with N₂ gas, SiCl₄ gas, H₂gas, and CH₄ gas were used to add high concentrations of oxygen atoms,silicon atoms, hydrogen atoms, and carbon atoms to the GaN crystal. InExample 12, a GaN crystal (group III nitride crystal) was grown in thesame way as in Example 11 except that the crystal growth rate was 90μm/h. Table III summarizes the results.

TABLE III Example 5 Example 6 Example 7 Example 8 Example 9 Example 10Example 11 Example 12 Group III Type of substrate GaN GaN GaN GaN GaNGaN GaN GaN nitride Plane orientation of (20-21) (20-21) (20-21) (20-21)(20-2-1) (20-2-1) (20-2-1) (20-2-1) crystal main plane substrate Surfaceroughness Ra of 5 5 5 5 5 5 5 5 main plane (mm) Surface roughness Ra of5 5 5 5 5 5 5 5 adjacent plane (mm) Group III Type of crystal GaN GaNGaN GaN GaN GaN GaN GaN nitride Crystal growth method HVPE HVPE HVPEHVPE HVPE HVPE HVPE HVPE crystal Crystal growth temperature 1020 10201020 1020 1020 1020 1020 1020 (° C.) Crystal growth rate (μm/hr) 70 8070 80 80 90 80 90 Plane orientation of (20-21) (20-21) (20-21) (20-21)(20-2-1) (20-2-1) (20-2-1) (20-2-1) main plane Presence of depression NoYes No Yes No Yes No Yes in main plane Full width at Region-on- 110 160110 170 80 160 90 165 half substrate maximum Region-on- 300 390 300 390290 395 290 380 of X-ray substrate- diffraction interface peak (arcsec)Threading Region-on- 1 × 10⁷  5 × 10⁷  2 × 10⁷  5 × 10⁷  1 × 10⁷  6 ×10⁷  2 × 10⁷  5 × 10⁷  dislocation substrate density of Region-on- 2 ×10⁷  7 × 10⁷  4 × 10⁷  8 × 10⁷  2 × 10⁷  7 × 10⁷  3 × 10⁷  8 × 10⁷  mainplane substrate- (cm⁻²) interface Planar defect density (cm⁻¹) 8.2 357.8 49 7.4 37 6.5 51 Carrier concentration ~1 × 10¹⁶  ~1 × 10¹⁶  4 ×10¹⁹ 4 × 10¹⁹ ~1 × 10¹⁶  ~1 × 10¹⁶  4 × 10¹⁹ 4 × 10¹⁹ (cm⁻³) Main [O](cm⁻³) 5 × 10¹⁵ 5 × 10¹⁵ 5 × 10¹⁹ 5 × 10¹⁹ 5 × 10¹⁵ 5 × 10¹⁵ 5 × 10¹⁹ 5× 10¹⁹ impurity [Si] (cm⁻³) 3 × 10¹⁴ 3 × 10¹⁴ 6 × 10¹⁸ 6 × 10¹⁸ 3 × 10¹⁴3 × 10¹⁴ 6 × 10¹⁸ 6 × 10¹⁸ atoms [H] (cm⁻³) 4 × 10¹⁶ 4 × 10¹⁶ 3 × 10¹⁸ 3× 10¹⁸ 4 × 10¹⁶ 4 × 10¹⁶ 3 × 10¹⁸ 3 × 10¹⁸ [C] (cm⁻³) 5 × 10¹⁵ 5 × 10¹⁵2 × 10¹⁸ 2 × 10¹⁸ 5 × 10¹⁵ 5 × 10¹⁵ 2 × 10¹⁸ 2 × 10¹⁸

Table III shows the following results in Examples 5 to 8, in which a GaNcrystal was grown on a GaN crystal substrate having a main plane with aplane orientation with an off-angle of five degrees or less with respectto {20-21}. In the grown GaN crystal having an oxygen atom concentrationbelow 1×10¹⁶ cm⁻³, a silicon atom concentration below 6×10¹⁴ cm⁻³, ahydrogen atom concentration below 6×10¹⁶ cm⁻³, and a carbon atomconcentration below 1×10¹⁶ cm⁻³, the planar defect density in the {0001}in-plane of the GaN crystal was as low as 8.2 cm⁻¹ at a crystal growthrate of 70 μm/h (less than 80 μm/h) (Example 5) and as high as 35 cm⁻¹at a crystal growth rate of 80 μm/h (80 μm/h or more) (Example 6).Likewise, in the grown GaN crystal having an oxygen atom concentrationabove 4×10¹⁹ cm⁻³, a silicon atom concentration above 5×10¹⁸ cm⁻³, ahydrogen atom concentration above 1×10¹⁸ cm⁻³, and a carbon atomconcentration above 1×10¹⁸ cm⁻³, the planar defect density in the {0001}plane of the GaN crystal was as low as 7.2 cm⁻¹ at a crystal growth rateof 70 μm/h (less than 80 μm/h) (Example 7) and as high as 49 cm⁻¹ at acrystal growth rate of 80 μm/h (80 μm/h or more) (Example 8).

Table III also shows the following results in Examples 9 to 12, in whicha GaN crystal was grown on a GaN crystal substrate having a main planewith a plane orientation with an off-angle of five degrees or less withrespect to {20-2-1}. In the grown GaN crystal having an oxygen atomconcentration below 1×10¹⁶ cm⁻³, a silicon atom concentration below6×10¹⁴ cm⁻³, a hydrogen atom concentration below 6×10¹⁶ cm⁻³, and acarbon atom concentration below 1×10¹⁶ cm⁻³, the planar defect densityin the {0001} plane of the GaN crystal was as low as 7.4 cm⁻¹ at acrystal growth rate of 80 μm/h (less than 90 μm/h) (Example 9) and ashigh as 37 cm⁻¹ at a crystal growth rate of 90 μm/h (90 μm/h or more)(Example 10). Likewise, in the grown GaN crystal having an oxygen atomconcentration above 4×10¹⁹ cm⁻³, a silicon atom concentration above5×10¹⁸ cm⁻³, a hydrogen atom concentration above 1×10¹⁸ cm⁻³, and acarbon atom concentration above 1×10¹⁸ cm⁻³, the planar defect densityin the {0001} plane of the GaN crystal was as low as 6.5 cm⁻¹ at acrystal growth rate of 80 μm/h (less than 90 μm/h) (Example 11) and ashigh as 51 cm⁻¹ at a crystal growth rate of 90 μm/h (90 μm/h or more)(Example 12).

Examples 13 to 20

In Examples 13 to 19, a GaN crystal was grown in the same way as inExample 12 except that the concentration of oxygen atoms added to theGaN crystal (group III nitride crystal) grown was altered. In Example20, a GaN crystal was grown in the same way as in Example 16 except thatthe crystal growth rate was 250 μm/h. Table IV summarizes the results.

TABLE IV Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- ple 13 ple 14ple 15 ple 16 ple 17 ple 18 ple 19 ple 20 Group III Type of substrateGaN GaN GaN GaN GaN GaN GaN GaN nitride Plane orientation of main plane(20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1)crystal Surface roughness Ra of main 5 5 5 5 5 5 5 5 substrate plane(mm) Surface roughness Ra of adjacent 5 5 5 5 5 5 5 5 plane (mm) GroupIII Type of crystal GaN GaN GaN GaN GaN GaN GaN GaN nitride Crystalgrowth method HVPE HVPE HVPE HVPE HVPE HVPE HVPE HVPE crystal Crystalgrowth temperature (° C.) 1020 1020 1020 1020 1020 1020 1020 1020Crystal growth rate (μm/hr) 90 90 90 90 90 90 90 250 Plane orientationof main plane (20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1)(20-2-1) (20-2-1) Presence of depression in main plane Yes Yes Yes YesYes Yes Yes Yes Full width at half Region-on-substrate 110 115 110 110120 125 110 95 maximum of X- Region-on-substrate- 365 350 360 365 370365 365 280 ray diffraction interface peak (arcsec) ThreadingRegion-on-substrate 2 × 10⁷  1 × 10⁷  1 × 10⁷  1 × 10⁷  1 × 10⁷  2 ×10⁷  4 × 10⁷  5 × 10⁶  dislocation Region-on-substrate- 4 × 10⁷  4 ×10⁷  4 × 10⁷  4 × 10⁷  4 × 10⁷  4 × 10⁷  5 × 10⁷  9 × 10⁶  density ofmain interface plane (cm⁻²) Planar defect density (cm⁻¹) 25 14.8 13.512.6 14.6 17.5 34 18.7 Carrier concentration (cm⁻³) 5 × 10¹⁸ 5 × 10¹⁸ 4× 10¹⁸ 5 × 10¹⁸ 1 × 10¹⁹ 4 × 10¹⁹ 6 × 10¹⁹ 6 × 10¹⁸ Main impurity [O](cm⁻³) 9 × 10¹⁵ 2 × 10¹⁶ 5 × 10¹⁶ 2 × 10¹⁸ 9 × 10¹⁸ 2 × 10¹⁹ 6 × 10¹⁹ 2× 10¹⁸ atoms [Si] (cm⁻³) 6 × 10¹⁸ 6 × 10¹⁸ 6 × 10¹⁸ 6 × 10¹⁸ 6 × 10¹⁸ 6× 10¹⁸ 6 × 10¹⁸ 6 × 10¹⁸ [H] (cm⁻³) 3 × 10¹⁸ 3 × 10¹⁸ 3 × 10¹⁸ 3 × 10¹⁸3 × 10¹⁸ 3 × 10¹⁸ 3 × 10¹⁸ 3 × 10¹⁸ [C] (cm⁻³) 2 × 10¹⁸ 2 × 10¹⁸ 2 ×10¹⁸ 2 × 10¹⁸ 2 × 10¹⁸ 2 × 10¹⁸ 2 × 10¹⁸ 2 × 10¹⁸

With reference to Table IV, the planar defect density in the {0001}plane of a GaN crystal grown on a GaN crystal substrate having a mainplane with a plane orientation with an off-angle of five degrees or lesswith respect to {20-2-1} was reduced even at a crystal growth rate of 90μm/h (90 μm/h or more) when the concentration of oxygen atom, which wasone of the impurity atoms in the GaN crystal, was preferably 1×10¹⁶ cm⁻³or more and 4×10¹⁹ cm⁻³ or less (Examples 14 to 18), more preferably5×10¹⁶ cm⁻³ or more and 1×10¹⁹ cm⁻³ or less (Examples 15 to 17), stillmore preferably 1×10¹⁷ cm⁻³ or more and 8×10¹⁸ cm⁻³ or less (Example16). An oxygen atom concentration of the GaN crystal of 1×10¹⁷ cm⁻³ ormore and 8×10¹⁸ cm⁻³ or less resulted in a low planar defect density inthe {0001} plane of the GaN crystal even when the crystal growth ratewas increased to 250 μm/h.

Examples 21 to 27

In Examples 21 to 27, a GaN crystal was grown in the same way as inExample 12 except that the concentration of silicon atoms added to theGaN crystal (group III nitride crystal) grown was altered. Table Vsummarizes the results.

TABLE V Exam- Exam- Exam- Exam- Example 21 Example 22 Example 23 ple 24ple 25 ple 26 ple 27 Group III Type of substrate GaN GaN GaN GaN GaN GaNGaN nitride Plane orientation of main plane (20-2-1) (20-2-1) (20-2-1)(20-2-1) (20-2-1) (20-2-1) (20-2-1) crystal Surface roughness Ra of mainplane (mm) 5 5 5 5 5 5 5 substrate Surface roughness Ra of adjacentplane (mm) 5 5 5 5 5 5 5 Group III Type of crystal GaN GaN GaN GaN GaNGaN GaN nitride Crystal growth method HVPE HVPE HVPE HVPE HVPE HVPE HVPEcrystal Crystal growth temperature (° C.) 1020 1020 1020 1020 1020 10201020 Crystal growth rate (μm/hr) 90 90 90 90 90 90 90 Plane orientationof main plane (20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1)(20-2-1) Presence of depression in main plane Yes Yes Yes Yes Yes YesYes Full width at half Region-on-substrate 120 120 110 120 120 118 140maximum of X-ray Region-on-substrate- 380 376 376 376 365 376 376diffraction peak interface (arcsec) Threading dislocationRegion-on-substrate 3 × 10⁷  2 × 10⁷  2 × 10⁷  2 × 10⁷  2 × 10⁷  2 ×10⁷  4 × 10⁷  density of main plane Region-on-substrate- 5 × 10⁷  4 ×10⁷  4 × 10⁷  4 × 10⁷  4 × 10⁷  4 × 10⁷  4 × 10⁷  (cm⁻²) interfacePlanar defect density (cm⁻¹) 23.9 18.4 16.3 15.3 17.1 18.4 32.3 Carrierconcentration (cm⁻³) 3 × 10¹⁹ 3 × 10¹⁹ 3 × 10¹⁹ 3 × 10¹⁹ 3 × 10¹⁹ 3 ×10¹⁹ 4 × 10¹⁹ Main impurity atoms [O] (cm⁻³) 5 × 10¹⁹ 5 × 10¹⁹ 5 × 10¹⁹5 × 10¹⁹ 5 × 10¹⁹ 5 × 10¹⁹ 5 × 10¹⁹ [Si] (cm⁻³) 5 × 10¹⁴ 7 × 10¹⁴ 2 ×10¹⁵ 1 × 10¹⁸ 2 × 10¹⁸ 4 × 10¹⁸ 6 × 10¹⁸ [H] (cm⁻³) 3 × 10¹⁸ 3 × 10¹⁸ 3× 10¹⁸ 3 × 10¹⁸ 3 × 10¹⁸ 3 × 10¹⁸ 3 × 10¹⁸ [C] (cm⁻³) 2 × 10¹⁸ 2 × 10¹⁸2 × 10¹⁸ 2 × 10¹⁸ 2 × 10¹⁸ 2 × 10¹⁸ 2 × 10¹⁸

With reference to Table V, the planar defect density in the {0001} planeof a GaN crystal grown on a GaN crystal substrate having a main planewith a plane orientation with an off-angle of five degrees or less withrespect to {20-2-1} was reduced even at a crystal growth rate of 90 μm/h(90 μm/h or more) when the concentration of silicon atom, which was oneof the impurity atoms in the GaN crystal, was preferably 6×10¹⁴ cm⁻³ ormore and 5×10¹⁸ cm⁻³ or less (Examples 22 to 26), more preferably 1×10¹⁵cm⁻³ or more and 3×10¹⁸ cm⁻³ or less (Examples 23 to 25), still morepreferably 1×10¹⁶ cm⁻³ or more and 1×10¹⁸ cm⁻³ or less (Example 24).

Examples 28 to 34

In Examples 28 to 34, a GaN crystal was grown in the same way as inExample 12 except that the concentration of hydrogen atoms added to theGaN crystal (group III nitride crystal) grown was altered. Table VIsummarizes the results.

TABLE VI Exam- Exam- Exam- Exam- Exam- Exam- Exam- ple 28 ple 29 ple 30ple 31 ple 32 ple 33 ple 34 Group III Type of substrate GaN GaN GaN GaNGaN GaN GaN nitride Plane orientation of main plane (20-2-1) (20-2-1)(20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1) crystal Surface roughnessRa of main plane (mm) 5 5 5 5 5 5 5 substrate Surface roughness Ra ofadjacent plane (mm) 5 5 5 5 5 5 5 Group III Type of crystal GaN GaN GaNGaN GaN GaN GaN nitride Crystal growth method HVPE HVPE HVPE HVPE HVPEHVPE HVPE crystal Crystal growth temperature (° C.) 1020 1020 1020 10201020 1020 1020 Crystal growth rate (μm/hr) 90 90 90 90 90 90 90 Planeorientation of main plane (20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1)(20-2-1) (20-2-1) Presence of depression in main plane Yes Yes Yes YesYes Yes Yes Full width at half maximum Region-on-substrate 120 122 125120 120 115 135 of X-ray diffraction peak Region-on-substrate- 375 370372 370 368 365 384 (arcsec) interface Threading dislocation densityRegion-on-substrate 2 × 10⁷  2 × 10⁷  2 × 10⁷  2 × 10⁷  2 × 10⁷  2 ×10⁷  2 × 10⁷  of main plane (cm⁻²) Region-on-substrate- 5 × 10⁷  5 ×10⁷  5 × 10⁷  5 × 10⁷  5 × 10⁷  5 × 10⁷  5 × 10⁷  interface Planardefect density (cm⁻¹) 22.3 17.6 16.1 16.1 16.3 17.5 28.1 Carrierconcentration (cm⁻³) 4 × 10¹⁹ 4 × 10¹⁹ 4 × 10¹⁹ 4 × 10¹⁹ 4 × 10¹⁹ 4 ×10¹⁹ 4 × 10¹⁹ Main impurity atoms [O] (cm⁻³) 5 × 10¹⁹ 5 × 10¹⁹ 5 × 10¹⁹5 × 10¹⁹ 5 × 10¹⁹ 5 × 10¹⁹ 5 × 10¹⁹ [Si] (cm⁻³) 6 × 10¹⁸ 6 × 10¹⁸ 6 ×10¹⁸ 6 × 10¹⁸ 6 × 10¹⁸ 6 × 10¹⁸ 6 × 10¹⁸ [H] (cm⁻³) 5 × 10¹⁶ 7 × 10¹⁶ 1× 10¹⁷ 7 × 10¹⁷ 8 × 10¹⁷ 1 × 10¹⁸ 2 × 10¹⁸ [C] (cm⁻³) 2 × 10¹⁸ 2 × 10¹⁸2 × 10¹⁸ 2 × 10¹⁸ 2 × 10¹⁸ 2 × 10¹⁸ 2 × 10¹⁸

With reference to Table VI, the planar defect density in the {0001}plane of a GaN crystal grown on a GaN crystal substrate having a mainplane with a plane orientation with an off-angle of five degrees or lesswith respect to {20-2-1} was reduced even at a crystal growth rate of 90μm/h (90 μm/h or more) when the concentration of hydrogen atom, whichwas one of the impurity atoms in the GaN crystal, was preferably 6×10¹⁶cm⁻³ or more and 1×10¹⁸ cm⁻³ or less (Examples 29 to 33), morepreferably 1×10¹⁷ cm⁻³ or more and 9×10¹⁷ cm⁻³ or less (Examples 30 to32), still more preferably 2×10¹⁷ cm⁻³ or more and 7×10¹⁷ cm⁻³ or less(Example 31).

Examples 35 to 41

In Examples 35 to 41, a GaN crystal was grown in the same way as inExample 12 except that the concentration of carbon atoms added to theGaN crystal (group III nitride crystal) grown was altered. Table VIIsummarizes the results.

TABLE VII Exam- Exam- Exam- Exam- Exam- Exam- Exam- ple 35 ple 36 ple 37ple 38 ple 39 ple 40 ple 41 Group III Type of substrate GaN GaN GaN GaNGaN GaN GaN nitride Plane orientation of main plane (20-2-1) (20-2-1)(20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1) crystal Surface roughnessRa of main plane (mm) 5 5 5 5 5 5 5 substrate Surface roughness Ra ofadjacent plane (mm) 5 5 5 5 5 5 5 Group III Type of crystal GaN GaN GaNGaN GaN GaN GaN nitride Crystal growth method HVPE HVPE HVPE HVPE HVPEHVPE HVPE crystal Crystal growth temperature (° C.) 1020 1020 1020 10201020 1020 1020 Crystal growth rate (μm/hr) 90 90 90 90 90 90 90 Planeorientation of main plane (20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1)(20-2-1) (20-2-1) Presence of depression in main plane Yes Yes Yes YesYes Yes Yes Full width at half maximum Region-on-substrate 125 120 110110 115 120 125 of X-ray diffraction peak Region-on-substrate- 378 375375 375 370 370 378 (arcsec) interface Threading dislocation densityRegion-on-substrate 1 × 10⁷  1 × 10⁷  1 × 10⁷  1 × 10⁷  1 × 10⁷  1 ×10⁷  2 × 10⁷  of main plane (cm⁻²) Region-on-substrate- 4 × 10⁷  4 ×10⁷  4 × 10⁷  4 × 10⁷  4 × 10⁷  4 × 10⁷  4 × 10⁷  interface Planardefect density (cm⁻¹) 25.5 19.7 17.4 16 17.8 18.6 31.1 Carrierconcentration (cm⁻³) 5 × 10¹⁹ 5 × 10¹⁹ 5 × 10¹⁹ 5 × 10¹⁹ 5 × 10¹⁹ 5 ×10¹⁹ 5 × 10¹⁹ Main impurity atoms [O] (cm⁻³) 5 × 10¹⁹ 5 × 10¹⁹ 5 × 10¹⁹5 × 10¹⁹ 5 × 10¹⁹ 5 × 10¹⁹ 5 × 10¹⁹ [Si] (cm⁻³) 6 × 10¹⁸ 6 × 10¹⁸ 6 ×10¹⁸ 6 × 10¹⁸ 6 × 10¹⁸ 6 × 10¹⁸ 6 × 10¹⁸ [H] (cm⁻³) 3 × 10¹⁸ 3 × 10¹⁸ 3× 10¹⁸ 3 × 10¹⁸ 3 × 10¹⁸ 3 × 10¹⁸ 3 × 10¹⁸ [C] (cm⁻³) 8 × 10¹⁵ 2 × 10¹⁶6 × 10¹⁶ 3 × 10¹⁷ 8 × 10¹⁷ 1 × 10¹⁸ 3 × 10¹⁸

With reference to Table VII, the planar defect density in the {0001}plane of a GaN crystal grown on a GaN crystal substrate having a mainplane with a plane orientation with an off-angle of five degrees or lesswith respect to {20-2-1} was reduced even at a crystal growth rate of 90μm/h (90 μm/h or more) when the concentration of carbon atom, which wasone of the impurity atoms in the GaN crystal, was preferably 1×10¹⁶ cm⁻³or more and 1×10¹⁸ cm⁻³ or less (Examples 36 to 40), more preferably5×10¹⁶ cm⁻³ or more and 9×10¹⁷ cm⁻³ or less (Examples 37 to 39), stillmore preferably 9×10¹⁶ cm⁻³ or more and 7×10¹⁷ cm⁻³ or less (Example38).

Examples 42 to 47

In Examples 42 to 47, a GaN crystal was grown in the same way as inExample 12 except that the concentration of an impurity atom added tothe GaN crystal (group III nitride crystal) grown was adjusted tosatisfy two of the oxygen atom concentration of 1×10¹⁶ cm⁻³ or more and4×10¹⁹ cm⁻³ or less, the silicon atom concentration of 6×10¹⁴ cm⁻³ ormore and 5×10¹⁸ cm⁻³ or less, the hydrogen atom concentration of 6×10¹⁶cm⁻³ or more and 1×10¹⁸ cm⁻³ or less, and the carbon atom concentrationof 1×10¹⁶ cm⁻³ or more and 1×10¹⁸ cm⁻³ or less. Table VIII summarizesthe results.

TABLE VIII Exam- Exam- Example 42 Example 43 Example 44 Example 45 ple46 ple 47 Group III Type of substrate GaN GaN GaN GaN GaN GaN nitridePlane orientation of main plane (20-2-1) (20-2-1) (20-2-1) (20-2-1)(20-2-1) (20-2-1) crystal Surface roughness Ra of main plane (mm) 5 5 55 5 5 substrate Surface roughness Ra of adjacent plane (mm) 5 5 5 5 5 5Group III Type of crystal GaN GaN GaN GaN GaN GaN nitride Crystal growthmethod HVPE HVPE HVPE HVPE HVPE HVPE crystal Crystal growth temperature(° C.) 1020 1020 1020 1020 1020 1020 Crystal growth rate (μm/hr) 90 9090 90 90 90 Plane orientation of main plane (20-2-1) (20-2-1) (20-2-1)(20-2-1) (20-2-1) (20-2-1) Presence of depression in main plane Yes YesYes Yes Yes Yes Full width at half maximum of Region-on-substrate 90 8895 84 80 80 X-ray diffraction peak Region-on-substrate- 310 280 320 240210 220 (arcsec) interface Threading dislocation densityRegion-on-substrate 4 × 10⁶  4 × 10⁶  6 × 10⁶  3 × 10⁶  3 × 10⁶  3 ×10⁶  of main plane (cm⁻²) Region-on-substrate- 9 × 10⁶  8 × 10⁶  1 ×10⁷  7 × 10⁶  7 × 10⁶  6 × 10⁶  interface Planar defect density (cm⁻¹) 67.3 6.7 10 9.6 11.8 Carrier concentration (cm⁻³) 1 × 10¹⁸ 4 × 10¹⁸ 6 ×10¹⁸ 5 × 10¹⁹ 5 × 10¹⁹ 5 × 10¹⁹ Main impurity atoms [O] (cm⁻³) 2 × 10¹⁸2 × 10¹⁸ 2 × 10¹⁸ 5 × 10¹⁹ 5 × 10¹⁹ 5 × 10¹⁹ [Si] (cm⁻³) 1 × 10¹⁸ 6 ×10¹⁸ 6 × 10¹⁸ 1 × 10¹⁸ 1 × 10¹⁸ 6 × 10¹⁸ [H] (cm⁻³) 3 × 10¹⁸ 7 × 10¹⁷ 3× 10¹⁸ 7 × 10¹⁷ 3 × 10¹⁸ 7 × 10¹⁷ [C] (cm⁻³) 2 × 10¹⁸ 2 × 10¹⁸ 3 × 10¹⁷2 × 10¹⁸ 3 × 10¹⁷ 3 × 10¹⁷

With reference to Table VIII, the planar defect density in the {0001}plane of a GaN crystal grown on a GaN crystal substrate having a mainplane with a plane orientation with an off-angle of five degrees or lesswith respect to {20-2-1} was greatly reduced even at a crystal growthrate of 90 μm/h (90 μm/h or more) when two of the impurity atomconcentrations, that is, the oxygen atom concentration, the silicon atomconcentration, the hydrogen atom concentration, and the carbon atomconcentration, of the GaN crystal were in the predetermined rangedescribed above (Examples 42 to 47).

Examples 48 to 51

In Examples 48 to 51, a GaN crystal was grown in the same way as inExample 12 except that the concentration of an impurity atom added tothe GaN crystal (group III nitride crystal) grown was adjusted tosatisfy three of the oxygen atom concentration of 1×10¹⁶ cm⁻³ or moreand 4×10¹⁹ cm⁻³ or less, the silicon atom concentration of 6×10¹⁴ cm⁻³or more and 5×10¹⁸ cm⁻³ or less, the hydrogen atom concentration of6×10¹⁶ cm⁻³ or more and 1×10¹⁸ cm⁻³ or less, and the carbon atomconcentration of 1×10¹⁶ cm⁻³ or more and 1×10¹⁸ cm⁻³ or less. Table IXsummarizes the results.

Examples 52 and 53

In Example 52, a GaN crystal was grown in the same way as in Example 12except that the concentration of an impurity atom added to the GaNcrystal (group III nitride crystal) grown was adjusted to satisfy all(four) of the oxygen atom concentration of 1×10¹⁶ cm⁻³ or more and4×10¹⁹ cm⁻³ or less, the silicon atom concentration of 6×10¹⁴ cm⁻³ ormore and 5×10¹⁸ cm⁻³ or less, the hydrogen atom concentration of 6×10¹⁶cm⁻³ or more and 1×10¹⁸ cm⁻³ or less, and the carbon atom concentrationof 1×10¹⁶ cm⁻³ or more and 1×10¹⁸ cm⁻³ or less. In Example 53, a GaNcrystal was grown in the same way as in Example 52 except that thecrystal growth rate was 250 μm/h. Table IX summarizes the results.

TABLE IX Exam- Exam- Example 48 Example 49 Example 50 Example 51 ple 52ple 53 Group III Type of substrate GaN GaN GaN GaN GaN GaN nitride Planeorientation of main plane (20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1)(20-2-1) crystal Surface roughness Ra of main plane (mm) 5 5 5 5 5 5substrate Surface roughness Ra of adjacent plane (mm) 5 5 5 5 5 5 GroupIII Type of crystal GaN GaN GaN GaN GaN GaN nitride Crystal growthmethod HVPE HVPE HVPE HVPE HVPE HVPE crystal Crystal growth temperature(° C.) 1020 1020 1020 1020 1020 1020 Crystal growth rate (μm/hr) 90 9090 90 90 250 Plane orientation of main plane (20-2-1) (20-2-1) (20-2-1)(20-2-1) (20-2-1) (20-2-1) Presence of depression in main plane Yes YesYes Yes Yes Yes Full width at half maximum of Region-on-substrate 80 7774 80 65 70 X-ray diffraction peak Region-on-substrate- 160 135 120 19080 95 (arcsec) interface Threading dislocation densityRegion-on-substrate 8 × 10⁵  6 × 10⁵  6 × 10⁵  7 × 10⁵  2 × 10⁵  4 ×10⁵  of main plane (cm⁻²) Region-on-substrate- 5 × 10⁶  3 × 10⁶  4 ×10⁶  6 × 10⁶  2 × 10⁶  3 × 10⁶  interface Planar defect density (cm⁻¹)3.8 3.6 3.2 4.9 0.3 0.8 Carrier concentration (cm⁻³) 1 × 10¹⁸ 7 × 10¹⁸ 1× 10¹⁸ 5 × 10¹⁹ 1 × 10¹⁸ 4 × 10¹⁸ Main impurity atoms [O] (cm⁻³) 2 ×10¹⁸ 2 × 10¹⁸ 2 × 10¹⁸ 5 × 10¹⁹ 2 × 10¹⁸ 2 × 10¹⁸ [Si] (cm⁻³) 1 × 10¹⁸ 6× 10¹⁸ 1 × 10¹⁸ 1 × 10¹⁸ 1 × 10¹⁸ 1 × 10¹⁸ [H] (cm⁻³) 7 × 10¹⁷ 7 × 10¹⁷3 × 10¹⁸ 7 × 10¹⁷ 7 × 10¹⁷ 7 × 10¹⁷ [C] (cm⁻³) 2 × 10¹⁸ 3 × 10¹⁷ 3 ×10¹⁷ 3 × 10¹⁷ 3 × 10¹⁷ 3 × 10¹⁷

With reference to Table IX, the planar defect density in the {0001}plane of a GaN crystal grown on a GaN crystal substrate having a mainplane with a plane orientation with an off-angle of five degrees or lesswith respect to {20-2-1} was more greatly reduced even at a crystalgrowth rate of 90 μm/h (90 μm/h or more) when three of the impurity atomconcentrations, that is, the oxygen atom concentration, the silicon atomconcentration, the hydrogen atom concentration, and the carbon atomconcentration, of the GaN crystal were in the predetermined rangedescribed above (Examples 48 to 51). The planar defect density in the{0001} plane of the GaN crystal was still more greatly reduced when all(four) of the impurity atom concentrations, that is, the oxygen atomconcentration, the silicon atom concentration, the hydrogen atomconcentration, and the carbon atom concentration, of the GaN crystalwere in the predetermined range described above (Example 52).Furthermore, the planar defect density in the {0001} plane of the GaNcrystal was very low even at a crystal growth rate as high as 250 μm/hwhen all (four) of the impurity atom concentrations, that is, the oxygenatom concentration, the silicon atom concentration, the hydrogen atomconcentration, and the carbon atom concentration, of the GaN crystalwere in the predetermined range described above.

Examples 54 and 55

In Example 54, a GaN crystal was grown in the same way as in Example 52except that the GaN crystal (group III nitride crystal) prepared inExample 52 was cut along planes parallel to a main plane of a GaNcrystal substrate (group III nitride substrate), the main planes wereground and polished to produce a plurality of additional GaN crystalsubstrates (additional group III nitride crystal substrates) having athickness of 1 mm and an average roughness Ra of the main plane of 5 nm,a crystal was grown on the (20-21) main plane of the second additionalGaN crystal substrate from the bottom, and the crystal growth rate was140 μm/h. In Example 55, a GaN crystal was grown in the same way as inExample 52 except that the GaN crystal (group III nitride crystal)prepared in Example 52 was cut along planes parallel to a main plane ofa GaN crystal substrate (group III nitride substrate), the main planeswere ground and polished to produce a plurality of additional GaNcrystal substrates (additional group III nitride crystal substrates)having a thickness of 1 mm and an average roughness Ra of the main planeof 5 nm, a crystal was grown on the (20-21) main plane of the secondadditional GaN crystal substrate from the bottom, and the crystal growthrate was 150 μm/h. Table X summarizes the results.

TABLE X Example 54 Example 55 Group III Type of substrate Substrateobtained from GaN Substrate obtained from GaN nitride crystal preparedin Example 52 crystal prepared in Example 52 crystal (second frombottom) (second from bottom) substrate Plane orientation of main plane(20-2-1) (20-2-1) Surface roughness Ra of main plane (mm)  5  5 Surfaceroughness Ra of adjacent plane (mm)  5  5 Group III Type of crystal GaNGaN nitride Crystal growth method HVPE HVPE crystal Crystal growthtemperature (° C.) 1020  1020  Crystal growth rate (μm/hr) 140  150 Plane orientation of main plane (20-2-1) (20-2-1) Presence of depressionin main plane No Yes Full width at half maximum of X-ray Region-on- 6570 diffraction peak (arcsec) substrate Region-on- 80 95 substrate-interface Threading dislocation density of main plane Region-on- 2 ×10⁵  4 × 10⁵  (cm⁻²) substrate Region-on- 2 × 10⁶  3 × 10⁶  substrate-interface Planar defect density (cm⁻¹)   0.3   0.3 Carrier concentration(cm⁻³) 4 × 10¹⁹ 1 × 10¹⁸ Main impurity atoms [O](cm⁻³) 5 × 10¹⁹ 2 × 10¹⁸[Si](cm⁻³) 6 × 10¹⁸ 1 × 10¹⁸ [H](cm⁻³) 3 × 10¹⁸ 7 × 10¹⁷ [C](cm⁻³) 2 ×10¹⁸ 3 × 10¹⁷

With reference to Table X, as compared with the growth of a GaN crystal,the planar defect density in the {0001} plane of a GaN crystal could bemarkedly reduced in the growth of an additional GaN crystal (anadditional group III nitride crystal) while the crystal growth face waskept flat up to a higher crystal growth rate (below 150 μm/h) using anadditional GaN crystal substrate (an additional group III nitridecrystal) prepared from a GaN crystal (group III nitride crystal)(Example 54). Even at the crystal growth rate at which facets wereformed on the crystal growth face, the planar defect density in the{0001} plane of the GaN crystal could be markedly reduced when all(four) of the impurity atom concentrations, that is, the oxygen atomconcentration, the silicon atom concentration, the hydrogen atomconcentration, and the carbon atom concentration, of the GaN crystalwere in the predetermined range described above.

It is to be understood that the embodiments and examples disclosedherein are illustrated by way of example and not by way of limitation inall respects. The scope of the present invention is defined by theappended claims rather than by the description preceding them. Allchanges that fall within the scope of the claims and the equivalencethereof are therefore intended to be embraced by the claims.

Industrial Applicability

Group III nitride crystals produced by a production method according tothe present invention can be used in light emitting devices (such aslight-emitting diodes and laser diodes), electronic devices (such asrectifiers, bipolar transistors, field-effect transistors, and highelectron mobility transistors (HEMT)), semiconductor sensors (such astemperature sensors, pressure sensors, radiation sensors, andvisible-ultraviolet photodetectors), surface acoustic wave (SAW)devices, acceleration sensors, micro electro mechanical systems (MEMS)components, piezoelectric vibrators, resonators, or piezoelectricactuators.

Reference Signs List

1 Group III nitride bulk crystal, 10 p, 10 q, 20 p Group III nitridecrystal substrate, 10 pm, 10 qm, 20 m, 20 pm, 30 m Main plane, 10 pt, 10qt Contact surface, 20, Group III nitride crystal, 20 g, 30 g Crystalgrowth face, 20 gf, 20 mf, 30 gf, 30 mf Facet, 20 s, 30 sRegion-on-substrate, 20 t, 30 t Region-on-substrate-interface, 20 tcVertical plane, 20 v, 30 v Depression, 90 Base substrate, 91 Mask layer,91 w Window

The invention claimed is:
 1. A group III nitride crystal characterizedby the following properties: having a main plane with acrystal-geometrically equivalent plane orientation selected from thegroup consisting of {20-21}, {20-2-1}, {22-41}, and {22-4-1}; anoxygen-atom concentration of between 1×10¹⁶ cm⁻³ and 4×10¹⁹ cm⁻³inclusive; a silicon-atom concentration of between 6×10¹⁴ cm⁻³ and5×10¹⁸ cm⁻³ inclusive; a hydrogen-atom concentration of between 6×10¹⁶cm⁻³ and 1×10¹⁸ cm⁻³ inclusive; a carbon-atom concentration of between1×10¹⁶ cm⁻³ and 1×10¹⁸ cm⁻³ inclusive; and a planar defect density ofbetween 0.3 and 51 defects/cm in a cross-section through the crystalperpendicular to either the <1-210>direction or to the <10-10>direction.2. The group Ill nitride crystal according to claim 1, wherein the mainplane has an area of 10 cm² or more.
 3. A method for producing the groupIII nitride crystal of claim 1, comprising the steps of: cutting aplurality of Group III nitride crystal substrates having a main planefrom a Group III nitride bulk crystal, the main plane having a planeorientation with an off-angle of five degrees or less with respect to acrystal-geometrically equivalent plane orientation selected from thegroup consisting of {20-21}, {20-2-1}, {22-41}, and {22-4-1};transversely arranging the substrates adjacent to each other such thatthe main planes of the substrates are parallel to each other and each[0001] direction of the substrates coincides with each other; andgrowing on the main planes of the substrates a Group III nitride crystalhaving said oxygen-, silicon-, hydrogen- and carbon-atom concentrations.4. The method for producing a group Ill nitride crystal according toclaim 3, wherein the average roughness Ra of each contact surface of thesubstrates adjacent to each other is 50 nm or less.
 5. The method forproducing a group III nitride crystal according to claim 3, wherein themethod for growing the group III nitride crystal is a hydride vaporphase epitaxy method.
 6. The method for producing a group III nitridecrystal according to claim 3, wherein in the step of growing a group IIInitride crystal the group III nitride crystal is grown while the crystalgrowth face is kept flat.
 7. The method for producing a group IIInitride crystal according to claim 6, wherein in the step of growing agroup III nitride crystal on the main planes of the substrates, when theplane orientation of the main planes has an off-angle of five degrees orless with respect to {20-21}, the group III nitride crystal has a growthrate below 80 μm/h, when the plane orientation of the main planes has anoff-angle of five degrees or less with respect to {20-2-1}, the groupIII nitride crystal has a growth rate below 90 μm/h, when the planeorientation of the main planes has an off-angle of five degrees or lesswith respect to {22-41}, the group III nitride crystal has a growth ratebelow 60 μm/h, and when the plane orientation of the main planes has anoff-angle of five degrees or less with respect to {22-4-1}, the groupIII nitride crystal has a growth rate below 80 μm/h.
 8. The method forproducing a group III nitride crystal according to claim 3, furthercomprising the steps of: preparing an additional group III nitridecrystal substrate having a main plane from the group III nitridecrystal, the main plane having a plane orientation with an off-angle offive degrees or less with respect to a crystal-geometrically equivalentplane orientation selected from the group consisting of {20-21},{20-2-1}, {22-41}, and {22-4-1}; and growing an additional group IIInitride crystal on the main plane of the additional group III nitridecrystal substrate.